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Geant4 User's Guide for Toolkit Developers

1. 3 4 Hadronic Physics 3 4 1 Introduction Optimal exploitation of hadronic final states played a key role in successes of all recent collider experiment in HEP and the ability to use hadronic final states will continue to be one of the decisive issues during the analysis phase of the LHC experiments Monte Carlo programs like Geant4 facilitate the use of hadronic final states and have been developed for many years We give an overview of the Object Oriented frameworks for hadronic generators in Geant4 and illustrate the physics models underlying hadronic shower simulation on examples including the three basic types of modeling data driven parametrisation driven and theory driven modeling and their possible realisations in the Object Ori ented component system of Geant4 We put particular focus on the level of extendibility that can and has been achieved by our Russian dolls approach to Object Oriented design and the role and importance of the frameworks in a component system 3 4 2 Principal Considerations The purpose of this section is to explain the implementation frameworks used in and provided by Geant4 for hadronic shower simulation as in the 1 1 release of the program The implementation frameworks follow the Rus sian dolls approach to implementation framework design A top level very abstracting implementation framework provides the basic interface to the other Geant4 categories and fulfils the most general use case for hadro
2. BuildPhysicsTable 97 CalcEnergyCuts r Computelosa G4RangeVector LR nec E GetValuet G4LossVector PufValue GetValue G4Allocator PulVaue ton Globais t G4ParticleDefinition on 7 thePDGM Ga doubi En o theParticleNarne GaSting 1 Geronimi G4DynamicParticle 1 fhePDGEncoding Gaint 8 emere Manager GetMomentumDiection 1 transee a trom PhysicsProcess GetTatalEnergy 9 GetPolarizatiord a e 9 theParfeleTable 39 renes redeem oaa theDecayTable E i rai 0 1 2 a CO E EN ha G4ParticleTable M G4 DecayProducts G4DecayTable n PushProducts T Momentum setParentPartik sure ribi d Boost Figure 2 13 Particle classes G4ParticleTable G4ParticleMessenger entries setNewValue findParticle getCurrentValue findAntiParticle gt 1 insert GetParticleTable X E 04r q flterator ictiqnary Ly Y i G4Strinc 1 p uE F pe FP AM hin Sie GAPTbIDictio G4PTbleDi 0 n G4Particle 4 bags di e T Definition narylterator clenaly gt i KV y KP VP x nem rere RWTValHa RWTPtrSlis O s Dictionary jo shDictionar RP 4 from RWTook inom RWToolsj 4 T v RE Figure 2 14 Particle Table G4DecayTable SelectADecayChannel G4Dynamic G Lorentz o Ire Particle Rotation y Parent ie ns n trom Globak E ae f j patent parent e T j channels G4Allocator D d 6 LA ls i G4VD h
3. G4Element GetHadroniclnteraction ar a i Apply Yourself SetMinEnergy x 0 SetMaxEnergy DeActivateFor gt i f erar ori G4Material lt lt Concrete gt gt PA ConcreteModel Figure 3 3 Level 2 implementation framework of the hadronic category of Geant4 final state production aspect 36 Extending Toolkit Functionality lt lt Abstract gt gt G4HadronicProcess Aeeevyrtuabs GatMicrescepicCrossSactien deciriuvab gt PoststepCott Asgisterer exiHac onic imer action s isctopaFroductionGlobally unting aCountingd D Conaaies G4IsoParticleChange lt lt Purely Abstracts G4VisotopeProduction Ed Gattsctope lt lt Concrata gt gt G4NeutronlsotopeProduction Figure 3 4 Level 2 implementation framework of the hadronic category of Geant4 isotope production aspect The three parts are integrated in the GaHadronic Process class that serves as base class for all hadronic processes of particles in flight Cross sections Each hadronic process is derived from G4Hadronic Process which holds a list of cross section da ta sets The term data set is representing an object that encapsulates methods and data for calculating total cross sections for a given process in a certain range of validity The implementations may take any form It can be a simple equation as well as sophisticated parameterisations or evaluated data All cross s
4. It manages multiple graphics systems and defines three more concepts the scene G4Scene the scene handler base class G4VSceneHandler itself a sub class of G4VGraphicsScene and the viewer base class G4V Viewer see below G4VisManager is a singleton and an abstract class requiring the user to derive from it a concrete visualisation manager G4VisExecutive is provided see below Roles and structure of the visualisation manager are described in Chapter 8 of the User s Guide for Application Developers e G4VisExecutive A concrete visualisation manager that implements the virtual functions RegisterGraphic sSystems and RegisterModelFactories These functions must be in the users domain since the graphics sys tems and models that are instantiated by them are in many cases provided by the user graphics libraries etc It is therefore implemented as a hh icc combination that is designed to be included in the users code Of course the user may write his or her own e G4Scene The scene is a list if models for physical volumes axes hits trajectories etc see Section Sec tion 2 12 4 They are distinguished according to their lifetime run duration for physical volumes etc end of event for hits and trajectories etc The end of event models are only to be used when the Geant4 state indicates the end of event has been reached The scene has an extent G4VisExtent which is updated by the scene when a new model is added
5. The class G4VIntranuclearTransportModel provides registering mechanisms for concrete implementa tions of GAVPreCompound Model and provides concrete intra nuclear transports with the possibility of del egating pre compound decay to these models G4VPreCompoundModel provides a registering mechanism for compound decay through the G4VExcitation Handler interface and provides concrete implementations with the possibility of delegat ing the decay of a compound nucleus The concrete scenario of Ga TheoFS Generator using a dual parton model and a classical cascade which in turn uses an exciton pre compound model that delegates to an evaporation phase would be the following G4TheoFS Generator receives the conditions of the interaction a primary particle and a nucleus It asks the 39 Extending Toolkit Functionality dual parton model to perform the initial scatterings and return the final state along with the by then damaged nucleus The nucleus records all information on the damage sustained GATheoFS Generator forwards all information to the classical cascade that propagates the particles in the already damaged nucleus keeping track of interactions further damage to the nucleus etc Once the cascade assumptions break down the cascade will collect the information of the current state of the hadronic system like excitation energy and number of excited particles and interpret it as a pre compound system It delegates the decay of th
6. e RandFlat distribution class for flat random number generation It also provides methods to fill an array of flat random values given its size or shoot bits e RandExponential distribution class defining exponential random number distribution given a mean It also provides a method to fill an array of flat random values given its size e RandGauss distribution class defining Gauss random number distribution given a mean or specifying also a deviation It also provides a method to fill an array of flat random values given its size 18 Design and Function of Geant4 Categories e RandBreitWigner distribution class defining the Breit Wigner random number distribution It also provides a method to fill an array of flat random values given its size e RandPoisson distribution class defining Poisson random number distribution given a mean It also provides a method to fill an array of flat random values given its size RandEngine Bai 3 DRand48Engine HatArray RanluxEngine TWert setSeed A FlatArray setSeedei ray setSeed o n setSeexi setSeeds satends Se on p 10 0 HepJamesRandom Ld E fait Fi Fi RanecuEngine g HatArray HepRandomEngine ar ng et amp eed D 0 seiSceds nde HatArray U zetSeed tes grtSeed seiSeeds getSeeds gt 1 setSeed 0 setSeedsi 1 0 y Py theEngine ail HepRandom Flest fatArray getTheEngine get TheGe
7. for all particles user may change it in its G4VUserPhysicsList If the track has the flag IsGoodForTracking true this check will have no effect used mainly to track particles below threshold e The parentID and the process pointer which created this track are set The secondary track is added to the list of secondaries If it has 0 kinetic energy it is only added if it it invokes a rest process at the beginning of the tracking e The track is updated and its status is set according to what the process defined Design and Function of Geant4 Categories 2 4 5 Ordering of Methods of Physics Processes The ProcessManager of a particle is responsible for providing the correct ordering of process invocations G4SteppingManager invokes the processes at each phase just following the order given by the ProcessMan ager of the corresponding particle For some processes the order is important Geant4 provides by default the right ordering It is always possible for the user to choose the order of process invocations at the initial set up phase of Geant4 This default ordering is the following 1 Ordering of GetPhysicalInteractionLength e In the loop of GetPhysicalInteractionLength of AlongStepDolt the Transportation process has to be in voked at the end e In the loop of GetPhysicalInteractionLength of AlongStepDolt the Multiple Scattering process has to be invoked just before the Transportation process 2 Ordering of Dolts e There is only
8. where XXX is your choice as above and make the modifications to pode Ga To do this simply instantiate and register for example visManager gt RegisterGraphicsSystem new G4XXX before visMan ager Initialise 42 Extending Toolkit Functionality e source visualization management include G4VisExecutive icc e config GAVIS BUILD gmk e config GAVIS USE gmk 3 5 1 1 1 Graphics driver templates in the xxx sub category You may use the following templates to help you get started writing a graphics driver The word template is used in the ordinary sense of the word they are not C templates e GAXXX G4XXXSceneHandler G4XXXViewer Templates for the simplest possible graphics driver These would be suitable for an immediate driver i e one which renders each object immediately to a screen Of course if the view needs re drawing as for example after a change of viewpoint the viewer requests a re issue of drawn objects e GAXXXFile G4XXXFileSceneHandler G4XXXFileViewer Templates for a file writing graphics driver The particular features are delayed opening of the file on receipt of the first item rewinding file on ClearView to simulate the clearing of views and prevent the duplication of material in the file closing of the file on ShowView which may also trigger the launch of a browser There are various degrees of sophistication in for example the allocation of filenames see FukuiRen
9. For example someone can describe DetectorAbc s field by creating a class DetectorAbcField that derives from your NewField class DetectorAbcField public NewField publie void MyFieldGradient GetFieldValue const double Point 3 double pField They then implement the function GetFieldValue void MyFieldGradient GetFieldValue const double Point 3 double pField We expect pField to point to pField 9 This amp the order of the components of pField is your own convention We calculate the value of pField at Point A new Equation of Motion for the new Field Once you have created a new type of field you must create an Equation of Motion for this Field This is required in order to obtain the force that a particle feels To do this you must inherit from G4Mag EqRhs and create your own equation of motion that understands your field In it you must implement the virtual function EvaluateRhsGivenB Given the value of the field this function calculates the value of the generalised force This is the only function that a subclass must define virtual void EvaluateRhsGivenB const G4double yl const G4double B 3 G4double dydx const 0 In particular the derivative vector dydx is a vector with six components The first three are the derivative of the position with respect to the curve length Thus they should set equal to the normalised velocity which is components 3 4 and 5 of y dydx 0 dyd
10. a use relation to G4ProcessManager and G4ParticleChange in the physics processes class category e G4Track the class G4Track represents a particle which is pushed by G4SteppingManager It holds information required for stepping a particle for example the current position the time since the start of step ping the identification of the geometrical volume which contains the particle etc Dynamic information such as particle momentum and energy is held in the class through a pointer to the G4DynamicParticle class Static information such as the particle mass and charge is stored in the G4DynamicParticle class through the pointer to the G4ParticleDefinition class Here the aggregation hierarchical design is extensively employed to maintain high tracking performance e G4TrajectoryPoint and G4Trajectory the class GATra jectoryPoint holds the state of the particle after propagating one step Among other things it includes information on space time energy momentum and geometrical volumes G4Trajectory aggregates all G4TrajectoryPoint objects which belong to the particle being propagat ed G4TrackingManager takes care of adding the G4TrajectoryPoint toa G4Trajectory object if the user requested it see Geant4 User s Guide For Application Developers The life ofa G4Trajectory object spans an event contrary to G4Track objects which are deleted from memory after being processed e G4UserTrackingAction and G4UserSteppingAction G4UserTracking
11. amp p const G4ThreeVector amp v const G4bool calcNorm false G4bool validNorm 0 G4ThreeVector n 0 Return distance along the normalised vector v to the shape from a point at an offset p inside or on the surface of the shape Intersections with surfaces when the point is not greater than kCarTolerance 2 from a surface must be ignored If calcNorm is true then it must also set validNorm to either If calcNorm is false then validNorm and n are unused G4bool CalculateExtent const EAxis pAxis const G4VoxelLimits amp pVoxelLimit const G4AffineTransform amp pTransform G4double amp pMin G4double amp pMax const Calculate the minimum and maximum extent of the solid when under the specified transform and within the specified limits If the solid is not intersected by the region return false else return true G4GeometryType GetEntityType const Provide identification of the class of an object required for persistency and STEP interface std ostream amp StreamInfo std ostream amp os const Should dump the contents of the solid to an output stream The method G4double GetCubicVolume 29 Extending Toolkit Functionality should be implemented for every solid in order to cache the computed value and therefore reuse it for future calls to the method and to eventually implement a precise computation of the solid s volume If the method will not be overloaded the default implementation from the ba
12. before drawing the trajectories to achieve this 3 There is an option to accumulate trajectories across events and runs see commands vis scene endOfEventAction and vis Scene endOfRunAction 47 Extending Toolkit Functionality If the driver does not have a graphical database or does not distinguish between transient and persistent objects it must emulate ClearTransientStore Typically it must erase everything including the detector and re draw the detector and other run duration objects ready for the transients to be added File writing drivers must rewind the output file Typically void G4HepRepFileSceneHandler ClearTransientStore G4VSceneHandler ClearTransientStore This is typically called after an update and before drawing hits of the next event To simulate the clearing of transients hits etc the detector is redrawn if fpViewer fpViewer SetView fpViewer ClearView fpViewer DrawView ClearView rewinds the output file and DrawView re draws the detector etc For smart drivers DrawView is smart enough to know not to redraw the detector etc unless the view parameters have changed significantly see Section 3 5 1 3 3 5 1 7 More about scene models Scene models conform to the G4VModel abstract interface Available models are listed and described there in varying detail Section 3 5 1 5 describes their use in some common command actions In the design of a n
13. digits Design and Function of Geant4 Categories Given the wide variety of Geant4 applications ways of describing detector sensitivity and the quantities to be stored in the hits and digits vary greatly This category therefore provides only abstract classes for both detector sensitivity and hits digits It also provides tools for organizing the hits digits into collections 2 6 2 Class Design e G4SensitiveDetectorManager a list of G4SensitiveDetectors e G4HitsStructure a tree like structure of G4Hit collections Each branch represents the hits in given sub de tector For example the first level of branches may consist of a tracker ECAL and HCAL while the second level in HCAL consists of the barrel and endcaps Finally the barrel may have phi slices Z slices etc e G4VSensitiveDetector an abstract class of all of sensitive volumes e G4HitsCollection a collection of hits Instantiates an RWCollection class e G4VHit this class has all the information about a particular hit caused by a single step e G4VDigitizer the class of objects which transform the hits deposited by particles into digitizations e G4DigitizerManager the single object dispatching common messages to individual digitizers e G4VDigi an abstract base class for all G4 digitizations This could be data as simple as a singe byte or as complex as an Ntuple G4DigiStructure digitizations are organized as a structure which could be anythi
14. fStopAndA Live It is on charge of selecting the rest process which has the shortest time before and then invoke it e To select the process with shortest tiem the AtRestGPIL method of all active processes is called Each process returns an lifetime and the minimum one is chosen This method returm also a G4ForceCondition flag to indicate if the process is forced or not Forced Corresponding AtRestDolt is forced NotForced Corre sponding AtRestDolt is not forced unless this process limits the step e Set the step length of current track and step to 0 e Invoke the AtRestDolt methods of the specified at rest process and they return the ParticleChange The order of invocation of processes is inverse to the order used for the GPIL methods After it for each process the following is executed e Set the current process as a process which defined this Step length e Update the G4Step information by using final state information of the track given by a physics process This is done through the UpdateStepForAtRest method of the ParticleChange e The secondaries from ParticleChange are stored to SecondaryList e Then for each secondary e tis checked if its kinetic energy is smaller than the energy threshold for the material In this case the particle is assigned a 0 kinetic energy and its energy is added as deposited energy of the parent track This check is only done if the flag ApplyCutFlag is set for the particle by default it is set to false
15. for each trajectory sceneHandler AddCompound called The scene handler may implement this virtual function or inherit Extending Toolkit Functionality Similarly the user may implement DrawTrajectory or inherit void G4VTrajectory DrawTrajectory G4int i mode const G4VVisManager pVVisManager G4VVisManager GetConcreteInstance if 0 pVVisManager pVVisManager gt DispatchToModel this i mode Thence the Draw method of the current trajectory model is invoked see Section 3 5 2 for details on trajectory models which in turn invokes Draw methods of the visualisation manager The resulting default sequence fora G4TrajectoriesModel is shown in Figure 3 11 DrawView ProcessView ProcessScene BeginModeling pModel gt DescribeYourselfTo this AddCompound trajectory trajectory DrawTrajectory DispatchToModel model Draw G4VisManager Draw BeginPrimitives objectTransform gt AddPrimitive EndPrimitives EndModeling Figure 3 11 The default sequence for a G4PhysicalVolumeModel 3 5 1 6 Dealing with transient objects Any visualisable object not defined in the run duration part of a scene is treated as transient This includes trajectories hits or anything drawn by the user through the G4VVisManager user level interface unless as part of a run duration model implementation A flag fRead
16. global category on external packages such as CLHEP STL and miscellaneous system utilities Within the management sub category are utility classes generally used within the Geant4 kernel They are for the most part uncorrelated with one another and include e G4Allocator e G4FastVector e G4ReferenceCountedHandle e G4PhysicsVector G4LPhysicsFreeVector G4PhysicsOrderedFreeVector e G4Timer e G4UserLimits e G4UnitsTable A general description of these classes is given in section 3 2 of the Geant4 User s Guide for Application Developers In applications where it is necessary to generate random numbers normally from the same engine in many dif ferent methods and parts of the program it is highly desirable not to rely on or require knowledge of the global objects instantiated By using static methods via a unique generator the randomness of a sequence of numbers is best assured Hence the use of a static generator has been introduced in the original design of HEPRandom as a project requirement in Geant4 2 11 2 Class Design Analysis and design of the HEPRandom module have been achieved following the Booch Object Oriented method ology Some of the original design diagrams in Booch notation are reported below Figure 2 17 is a general picture of the static class diagram e HepRandomEngine abstract class defining the interface for each Random engine Its pure virtual methods must be defined by its subclasses representing the
17. in the visualisation category under subdirectory visualisation XXX but they are not default registered graphics systems 2 There are several sets of classes described in more detail below A recommended approach is to copy the files that best match your graphics system to a new subdirectory with a name that suits your graphics system Then 1 Change the name of the files change the code XXX or XXXF ile etc as chosen to something that suits your graphics system Change XXX similarly in all files Change XXX similarly in name G4XXX in GNUmakefile Add your new subdirectory to SUBDIRS and SUBLIBS in visualisation GNUmakefile Look at the code and use it to build your visualisation driver You might also find it useful to look at ASCI ITree and VTree as an example of a minimal graphics driver Look at FukuiRenderer as an example of a driver which implements AddSolid methods for some solids Look at OpenGL as an example of a driver which implements a graphical database display lists and the machinery to decide when to rebuild OpenGL is complicated by the proliferation of combinations of the use or not of display lists for three win dow systems X windows X with motif interactive Microsoft Windows Win32 a total of six combina tions and much use is made of inheritance to avoid code duplication 6 If it requires external libraries introduce two new environment variables GAVIS BUILD XXX DRIVER and GAVIS USE XXX
18. pVisAtts visible GetVisAttributes if pVisAtts pVisAtts fpViewer GetViewParameters GetDefaultVisAttributes where visible denotes any visible object polyhedron circle etc There is a utility function G4V Viewer GetA pplicableVisAttributes which does this so an alternative is const G4VisAttributes pVisAtts fpViewer GetApplicableVisAttributes visible GetVisAttributes Confusingly there is a utility function G4VSceneHandler GetColour which also does this so if it s only colour you need the following suffices const G4Colour amp colour GetColour visible but equally well const G4VisAttributes pVisAtts fpViewer GetApplicableVisAttributes visible GetVisAttributes const G4Colour amp colour pVisAtts GetColour or even const G4VisAttributes pVisAtts visible GetVisAttributes if pVisAtts pVisAtts fpViewer GetViewParameters GetDefaultVisAttributes const G4Colour amp colour pVisAtts gt GetColour 2 12 6 1 2 Text Text is a special case because it has its own default vis attributes 24 Design and Function of Geant4 Categories const G4VisAttributes pVisAtts text GetVisAttributes if pVisAtts pVisAtts fpViewer GetViewParameters GetDefaultTextVisAttributes const G4Colour amp colour pVisAtts gt GetColour and there is a utility function G4V Scene Handler GetTextColour const G4Colour amp colour GetTextColour text 2 12 6 1 3 Soli
19. particle in a field or rectilinearly based on whether the particle is charged or not If your field affects non charged particles you must inherit from the G4Transportation andre implement the part of GetAlongStepPhysicalInteractionLength that decides whether the particles is affected by your force In particular the relevant section of code does the following Does the particle have an EM field force exerting upon it if particleCharge 0 0 fieldExertsForce this DoesGlobalFieldExist Future will can also check whether current volume s field is Zero or set by the user in the logical volume to be zero and you want it to ask whether it feels your force If for the sake of an example you wanted to see the effects of gravity on a heavy hypothetical particle you could say Does the particle have my field s force exerted on it if particle gt GetName VeryHeavyWIMP fieldExertsForce this DoesGlobalFieldExist For gravity After doing all these steps you will be able to see the effects of your force on a particle s motion Status of this chapter 10 06 02 partially re written by D H Wright 33 Extending Toolkit Functionality 14 11 02 spell check by P Arce 3 3 Physics Processes Adding a new electromagnetic process Adding a new hadronic process Status of this chapter 27 06 05 under construction Dec 2006 Conversion from latex to Docbook verson by K Amako
20. process non geometry items and distinguish between transient and permanent objects as above 3 5 1 2 Important Command Actions To help understand how the Geant4 Visualization System works here are a few important function invocation sequences that follow user commands For an explanation of the commands themselves see command guidance or the Control section of the Application Developers Guide For a fuller explanation of the functions see appropriate base class head files or Software Reference Manual vis viewer clear viewer ClearView Clears buffer or rewinds file viewer FinishView Swaps buffer double buffer systems vis viewer flush vis viewer refresh vis viewer update vis viewer rebuild viewer SetNeedKernelVisit true 43 Extending Toolkit Functionality e vis viewer refresh If the view is auto refresh this command is also invoked after vis view er create vis viewer rebuild ora change of view parameters vis viewer set etc viewer gt SetView Sets camera position etc viewer ClearView Clears buffer or rewinds file viewer DrawView Draws to screen or writes to file socket vis viewer update viewer ShowView Activates interactive windows or closes file and or triggers post processing vis scene notifyHandlers For each viewer of the current scene the equivalent of vis viewer refresh If flush is specifi
21. through registration 3 4 7 Level 5 Framework String De excitation Ga4ExcitedString GetPosition satPasiticn GetPartonLit lt lt Puraly Abstracts EA H aet4Mamentum Ga VStringF ragmertation 4 rsartParton SFragmantstrng Trans CentarotMass maligna 7 S ts Exnctect GotHadron lt lt Puraly Abstracts Ga4VFragmentatiorFunction Saat ightConezi lt lt Conciatas gt lt lt Concretes gt G40GSMFragmentation Gon GiLundStingFragmertation Gal Cone gt Ge C Z feGatLigttoa ni G4FeynmanFragmentation dyoeugniconsz J PGctLigntcor uz Figure 3 8 Level 5 implementation framework of the hadronic category of Geant4 string fragmentation aspect The use case of this level is that of a user or theoretical physicist wishing to understand the systematic effects involved in combining various fragmentation functions with individual types of string fragmentation Note that this framework level is meeting the current state of the art making extensions and changes of interfaces in subsequent releases likely Requirements 1 Allow the selection of fragmentation function Design and interfaces A base class for fragmentation functions GAVFragmentation Function is provided It declares the Get LightConeZ interface 41 Extending Toolkit Functionality Framework functionality The design is a basic Strategy The class diagram is shown in Figure 3 8 At t
22. tracking category G4TrackingManager is responsible for processing one track which it receives from the event manager G4TrackingManager aggregates the pointers to G4SteppingManager G4Trajectory and G4UserTrackingAction It also has a use relation to G4Track e G4SteppingManager plays an essential role in particle tracking It performs message passing to objects in all categories related to particle transport such as geometry and physics processes Its public method Step ping steers the stepping of the particle The algorithm employed in this method is basically the same as that in Geant3 The Geant4 implementation however relies on the inheritance hierarchy of the physics inter actions The hierarchical design of the physics interactions enables the stepping manager to handle them as abstract objects Hence the manager is not concerned with concrete interaction objects such as bremsstrahlung or pair creation The actual invocations of various interactions during the stepping are done through a dynam ic binding mechanism This mechanism shields the tracking category from any change in the design of the physics process classes including the addition or subtraction of new processes G4SteppingManager also aggregates the pointers to G4Navigator from the geometry category to the current G4Track and e the list of secondaries from the current track through a G4TrackVector to G4UserSteppingAction and to GAVSteppingVerbose It also has
23. 64Hadronic Interactionpro vides the functionality needed to define and enforce the applicability of a particular model Models inheriting from G4Hadronic Interaction can be restricted in applicability in projectile type and energy and can be acti vated deactivated for individual materials and elements This allows a user to use final state production models in arbitrary combinations and to write his own models for final state production The design is a variant of a Chain of Responsibility An example would be the likely CMS scenario the combination of low energy neutron transport with a quantum molecular dynamics QMD invariant phase space decay CHIPS and fast parametrised models for calorimeter materials with user defined modeling of interactions of spallation nucleons with the most abundant tracker and calorimeter materials Isotope production The G4HadronicProcess by default calculates the isotope production information from the final state giv en by the transport model In addition it provides a registering mechanism for isotope production models that run in parasitic mode to the transport models and inherit from GAVIsotope Production The registering mechanism behaves like a FILO stack again based on Chain of Responsibility The models will be asked for isotope production information in inverse order of registration The first model that returns a non NULL value will be applied In addition the G4Hadronic Process provides the basic inf
24. 7 User hit classes 10 Design and Function of Geant4 Categories G4VSensitiveDe tector W J 1 9 1 G4VReadOutG eometry e R buikl includetist 1 wo e excludeList n G4GRSVolume G4Sensitive ol irom Geometry umeList 0 n G4GRSSolid G4VPhysical p n rom Geometry Volume from Geometry nome y x G4LogicalVol da G4VTouchable ume From Geometry from Geometry Figure 2 8 Readout geometry Status of this chapter 27 06 05 section on design philosophy added from Geant4 general paper by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 7 Geometry 2 7 1 Design Philosopy The geometry category provides the ability to describe a geometrical structure and propagate particles efficiently through it This is done in part with the aid of two central concepts the logical and physical volumes A logical volume represents a detector element of a given shape which may contain other volumes and which may have other attributes It has access to other information which is independent of its phyisical location in the detector such as material and sensitive detector behavior A physical volume represents the spatial positioning or placement of the logical volume with respect to an enclosing mother logical volume Thus a hierarchical tree structure of volumes can be built with each volume containing smaller volumes which may not overlap Repetitive structures can be r
25. Action is a base class from which user actions at the beginning or end of tracking may be derived Similarly GAUserSteppingAction is a base class from which user actions at the beginning or end of each step may be derived 2 4 3 Tracking Algorithm The key classes for tracking in Geant4 are G4TrackingManager and G4SteppingManager The singleton object TrackingManager from G4TrackingManager keeps all information related to a particular track and it also manages all actions necessary to complete the tracking The tracking proceeds by pushing a particle by a step the length of which is defined by one of the active processes The TrackingManager object delegates management of each of the steps to the SteppingManager object This object keeps all information related to a particular step The public method ProcessOneTrack in G4TrackingManager is the key to managing the tracking while the public method Stepping is the key to managing one step The algorithms used in these methods are explained below ProcessOneTrack in G4TrackingManager 1 Actions before tracking the particle Clear secondary particle vector DN UA S AS Design and Function of Geant4 Categories Pre tracking user intervention process Construct a trajectory if it is requested Give SteppingManager the pointer to the track which will be tracked Inform beginning of tracking to physics processes Track the particle Step by Step while it is alive e Call Stepping
26. Allow to use or adapt any string parton or parton transport VNI 38 Extending Toolkit Functionality Allow to adapt event generators ex PYTHIAT state production in shower simulation Allow for combination of the above with any intra nuclear transport INT Allow stand alone use of intra nuclear transport Allow for combination of the above with any pre compound model Allow stand alone use of any pre compound model Allow for use of any evaporation code Allow for seamless integration of user defined components for any of the above DOS GN Bs O Design and interfaces To provide the above flexibility the following abstract base classes have been implemented e G4VHighEnergyGenerator e G4VIntranuclearTransportModel G4VPreCompoundModel e G4VExcitationHandler In addition the class G4TheoFS Generator is provided to orchestrate interactions between these classes The class diagram is shown in Figure 3 5 G4VHighEnergy Generator serves as base class for parton transport or parton string models and for Adapters to event generators This class declares two methods Scatter and GetWoundedNucleus The base class for INT inherits from G4Hadronic Interaction making any concrete implementation us able as a stand alone model In doing so it re declares the Appl yYoursel1f interface of G4Hadronic In teraction and adds a second interface Propagate for further propagation after high energy interactions Propa
27. Extent const EAxis pAxis const G4VoxelLimits amp pVoxelLimit const G4AffineTransform amp pTransform G4double amp pMin G4double amp pMax const G4GeometryType GetEntityType const Std ostream amp StreamInfo std ostream amp os const They must perform the following functions EInside Inside const G4ThreeVector amp p This method must return 28 Extending Toolkit Functionality e kOutside if the point at offset p is outside the shape boundaries plus Tolerance 2 e kSurface if the point is lt Tolerance 2 from a surface or e kInside otherwise G4ThreeVector SurfaceNormal const G4ThreeVector amp p Return the outwards pointing unit normal of the shape for the surface closest to the point at offset p G4double DistanceToIn const G4ThreeVector amp p Calculate distance to nearest surface of shape from an outside point p The distance can be an underestimate G4double DistanceToIn const G4ThreeVector amp p const G4ThreeVector amp v Return the distance along the normalised vector v to the shape from the point at offset p If there is no intersection return kInfinity The first intersection resulting from leaving a surface volume is discarded Hence this is tolerant of points on surface of shape G4double DistanceToOut const G4ThreeVector amp p Calculate distance to nearest surface of shape from an inside point The distance can be an underestimate G4double DistanceToOut const G4ThreeVector
28. Geant4 User s Guide for Toolkit Developers Version geant4 9 0 Published 29 June 2007 Geant4 Collaboration Geant4 User s Guide for Toolkit Developers by Geant4 Collaboration Version geant4 9 0 Published 29 June 2007 Table of Contents 1 Introduction 1 eet dias tivas pa s oia e Pie Do dead 1 1 1 Scope of this manual centered A tas aiii 1 1 2 How to use this manual e Dee tto rr HER seuss sects ERR eR pre fabes 1 1 3 User Requirements Document 200 0000 eee cee cece cee III HI ee hee herein rentre nenne 1 2 Design and Function of Geant4 Categories sss ee heme menm ment enm E aen 2 2 1 Introduction sico eerie Ue dee Urso ete Ee ERE RE ERA deer Or gest eg ue Eesha eats 2 2 2 R n oon eter Ded yr e REESE P eur ET RP ue rires 2 2 2 1 Design Philosophy repre tee ete rev pere e EL EE EUREN eee 2 2 22 Class Desi i reti tte P Pe Sato eth ere tp Potete Ett TG ede 2 2 3 EVEN i oed RE cd ennt pr PIER er Ee ee URS 2 2 3 1 Design Philosophy pisco tf rh SE Reed Re dee hr ERR EP En SERRE IRR 2 2 3 2 Class Design 2 dinner te EM UMEN DINER E IE SPEI 2 DA Tracking 2 A 3 2 4 1 Design Philosophy eerte ete treten in Gees 4 2 4 2 Class DESIGN PCM UT 4 2 4 3 Tracking Algorithm se esee lnea necu 5 2 4 4 Interaction with Physics Processes sssssssee Hm Hmm 6 2 4 5 Ordering of Methods of Physics Processes 8 2 5 PHYSICS PLOCESSES ss 25 cer dre er E Res vest cd Re rur E Tees FER P
29. IAT Pythia version 7 0 0 a proof of concept version M Bertini L Lonnblad T Sjorstrand LU TP 00 23 hep ph 0006152 May 2000 51
30. RR ESTEE 8 2 5 1 Design Philosophy eii eue EEE ES E EEEE EAEE EEE dress eede 8 2 52 Class Design 5x io dd eer n ee te cte E te et tere ones PORTER Ores 9 2 6 Hits and Digitization assess tano diner e vere vei een fer ege sese Pe vedete p re rete gEe dera 9 2 6 1 Design Philosophy rer ER E SEE PH EE ERR MER Hn ERR E Pre Pel ERE 9 2 6 2 Class Desigr 5 terre epe EIU ii 10 2 1 Geometry i eee P o D prete xe etel Patet epe ke diese ea Piece a detto 11 2 7 1 Design ule en P ess eon Lee SOAs A Neate a ae wa abe 11 2 1 2 Class Design cotilla 11 2 7 3 Additional Geometry Diagrams esses emere 13 2 8 Electromagnetic Fields tt asa Ii gse eee e bane E 14 2 9 Particles ii tetro STON eae A Rie E as 15 2 9 1 Design Philosophy A Ert peer ERE Fe ies E rte Re TRES EESTE T SS 15 2 9 2 Class Design iii ii 15 2 10 Materials 5 ei tai 17 2 10 1 Design Philosophy cesse eee Dian EE rica 17 2 10 2 Class DeSIgn iei ED rtr rrr Rb RD HRS 17 2 11 Global Usage csi ii ee de dis 18 2 11 1 Design Philosophy 2 ret err mter iaa rta mt 18 22 Class DSS OM cui ERR 18 2 12 Visualisation efe HERE tees Pores Pe REIR ISP P re A SEP 21 2 121 Design Philosophy idee ERIS EID EN 21 2 122 The Graphics Interfaces ere th rte rre dads tor ERR css rios h 21 2 12 3 The Geant4 Visualisation System sse 22 2 12 4 Modeling Sub category A dg CERERI EE BEER ERIS EER CER SERRE IRR 23 212 5 View parameters aior ene ag
31. The class G4ViewParameters has utility routines to assist this procedure it is strongly advised that toolkit developers writing a viewer should study the G4ViewParameters class whose header file contains much useful information also preserved in the Software Reference Manual The viewer is messaged by the vis manager when the user issues commands such as vis viewer re fresh This invokes methods such as SetView ClearView and Draw View A detailed description of the call sequences is given in Section 3 5 1 2 Section 3 5 1 5 Note there is no restriction on the number or type of scene handlers or viewers There may be several scene handlers processing the same or different scenes each with several viewers for example the same scene from differing viewpoints By defining a set of three C classes inheriting from the virtual base classes G4VGraphicsSystem G4VSceneHandler and G4VViewer an arbitrary graphics system can easily be plugged in to Geant4 The plugged in graphics system is then available for visualising detector simulations Together this set of three con crete classes is called a visualisation driver The DAWN File driver for example is the interface to the Fukui Renderer DAWN and is implemented by the following set of classes 1 G4DAWNFILE public G4VGraphicsSystem for creation of the scene handlers and viewers 2 G4DAWNFILESceneHandler public G4VSceneHandler for modeling 3D scenes 22 3 Design and Funct
32. ability 34 Extending Toolkit Functionality Design and interfaces Both requirements are implemented in a sub set of the tracking physics interface in Geant4 The class diagram is shown in Figure 3 1 Purely Abstract G4VProcess PostStepGetPhysicalinteractionLength S PostStepDolti AlongStepGetPhysical InteractionLength AlongStepDolt S AtRestGetPhysicalInteractionLength AtRestDol 7 Abstract Abstract G4VDiscreteProcess G4VRestProcess PostStepGetPhysicalinteractionLength V atrestGetPhysicalinteraction Length tStepDolt 3 on engnu r ostSipDont atFiestDolti lt lt Abstract gt gt G4HadronicProcess virtual GetMicroscopicCrossSection Y o artusl gt gt PostStepDolt Register me ChooseHadroricinteractiont GeneralPostStepDo t lt lt static gt gt GetlsotopeProductioninfo Register IsotopeProductionModel static EnablelsotopeProductionGlobally 5 statics Disable botopeProductionGlobally Ensnie sotopeCounting Disablelsotope Counting Figure 3 1 Level 1 implementation framework of the hadronic category of GEANT4 All processes have a common base class G4VP rocess from which a set of specialised classes are derived Three of them are used as base classes for hadronic processes for particles at rest G4VRestProcess for interactions in flight G4VDiscreteProcess and for processes like radioactive decay where the same
33. addGenerator generateOneEvent gimmeVertex G4OrderedV ector from BaseClass e generators h n GAD icParticle Si Pim dnt GaP irmaryVerian ynamicFarti ti Vert T gene man Venet Port Spector V ON vertex ime G4double amp particles insert G4UserPrimaryGen erator 1 LA p n G4ParticleDefinition G4DynamicParticle G4ParlicleGun from ParticieDefinition irom ParticleDefinition set particle definition set particle eneray 1 set particle momentum sel_particle_position e Fie luzerzkurazige HOSE2Ig40831 md Thu Aug 31 19 53 30 1995 Chez Diagram EventGenerator Main Figure 2 2 Event Generator Status of this chapter 27 06 05 design philosophy section added from Geant4 general paper by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 4 Tracking The tracking category manages the contribution of the processes to the evolution of a track s state and provides information in sensitive volumes for hits and digitization Design and Function of Geant4 Categories 2 4 1 Design Philosophy It is well known that the overall performance of a detector simulation depends critically on the CPU time spent propagating the particle through one step The most important consideration in the object design of the tracking category is maintaining high execution speed in the Geant4 simulation while utilizing the power of the object ori ented approach An extrem
34. c choices for physics generators and of specific solutions for storing the Monte Carlo truth G4Event avoids keeping any transient information which is not meaningful after event processing is complete Thus the user can store objects of this class for processing further down the program chain For performance reasons G4Event and its content classes are not persistent Instead the user must provide the transient to persistent conversion 2 3 2 Class Design e G4Event This class represents an event It is constructed and deleted by G4RunManager or its derived class Design and Function of Geant4 Categories e G4EventManager This class controls an event It must be a singleton and should be constructed by G4RunManager e G4VPrimaryGenerator the abstract base class of all of primary generators This class has only one pure virtual method GeneratePrimary Vertex which takes a G4Event object generates a primary vertex and as sociates primary particles with the vertex Booch diagrams for classes related to the event and event generator classes are shown in Figure 2 1 and Figure 2 2 A EVER loma las sbreTisjo Actisct Iapan iere Wir gelonter lor aic Ion oor Mine Palla A ae Mack ES p alar p Wut fa FAT apra Trem Tree tanas cal SD me e a erica His sse wesakiv OSE 4 AQ SI 1320043 199 Case tlegrsm Everz amp aragerie wt MSIN Figure 2 1 Event G4EventGenerator
35. cal volumes e co working with graphical user interfaces Because it is very difficult to respond to all of these requirements with only one built in visualiser an abstract interface was developed which supports several complementary graphics systems Here the term graphics system means either an application running as a process independent of Geant4 or a graphics library to be compiled with Geant4 A concrete implementation of the interface is called a visualisation driver which can use a graphics library directly communicate with an independent process via pipe or socket or simply write an intermediate file for a separate viewer 2 12 2 The Graphics Interfaces G4VVisManager All user code writes to the graphics systems through this pure abstract interface It contains Draw methods for all the graphics primitives in the graphics reps category G4Polyline G4Circle etc ge ometry objects through their base classes G4VSolid G4PhysicalVolume and G4LogicalVolume and hits and trajectories through their base classes G4V Hit and G4VTrajectory Since this is an abstract interface all user code must check that there exists a concrete instantiation of it A static method is provided so a typical user code fragment is G4VVisManager pVVisManager G4VVisManager GetConcreteInstance if pVVisManager pVVisManager gt Draw G4Circle Note that this allows the building an application without a concrete implementation for example fo
36. concrete Random engines e HepJamesRandom class inheriting from HepRandomEngine and defining a flat random number generator according to the algorithm described in F James Comp Phys Comm 60 1990 329 This class is instantiated by default as the default random engine DRand48Engine class inheriting from HepRandomEngine and defining a flat random number generator according to the drand48 and srand48 system functions from the C standard library e RandEngine class inheriting from HepRandomEngine and defining a flat random number generator accord ing to the rand and srand system functions from the C standard library e RanluxEngine class inheriting from HepRandomEngine and defining a flat random number generator ac cording to the algorithm described in F James Comp Phys Comm 60 1990 329 344 and originally imple mented in FORTRAN 77 as part of the MATHLIB HEP library It provides 5 different luxury levels 0 4 e RanecuEngine class inheriting from HepRandomEngine and defining a flat random number generator ac cording to the algorithm RANECU originally written in FORTRAN 77 as part of the MATHLIB HEP library It uses a table of seeds which provides uncorrelated couples of seed values e HepRandom the main class collecting all the methods defining the different random generators applied to HepRandomEngine It is a singleton class which all the distribution classes derive from This singleton is instantiated by default
37. derer or HepRepFile These templates also show the use of a specific AddSolid function whereby the specific parameters for example the dimensions of a G4Box can be accessed e GAXXXStored G4XXXStoredSceneHandler G4XXXStoredViewer Templates for a graphics driver with a store database The advantage of a store is that the view can be refreshed for example from a different viewpoint without a need to recompute It is up to the viewer to decide when a re computation is necessary They also show how to distinguish between permanent and transient objects see also Section Section 3 5 1 6 e GAXXXSG G4XXXSGSceneHandler G4XXXSGViewer Templates for a sophisticated graphics driver with a scene graph The scene graph following Open Inventor parlance is a tree of objects that dictates the order in which the objects are rendered It obviously lends itself to the rendering of the Geant4 geometry hierarchy For example the Open Inventor driver draws only the top level volumes unless made invisible by picking Thus the user can unwrap a branch of the geometry level by level This has performance benefits and gives the user significant and useful control over the view These classes show how to make a scene graph of drawn volumes i e the set of volumes that have not been culled Normally volumes marked invisible are culled i e not drawn Also the user may wish to limit the number of drawn volumes for performance reasons The drivers also have to
38. dron gt AddPrimitive pPolyhedron gt EndPrimitives sceneHandler PostAddSolid EndModeling 7 7 Figure 3 10 The default sequence for a G4PhysicalVolumeModel Note the sequence of calls at the core sceneHandler PreAddSolid theAT pVisAttribs pSol DescribeYourselfTo sceneHandler gt sceneHandler AddSolid this gt RequestPrimitives solid gt BeginPrimitives fpObjectTransformation gt pPolyhedron solid GetPolyhedron AddPrimitive pPolyhedron gt EndPrimitives sceneHandler PostAddSolid is reduced to sceneHandler PreAddSolid theAT pVisAttribs pSol DescribeYourselfTo sceneHandler gt sceneHandler AddSolid this sceneHandler PostAddSolid if the scene handler implements its own AddSolid Moreover the sequence BeginPrimitives fpObjectTransformation AddPrimitive pPolyhedron EndPrimitives can be invoked without a prior PreAddSolid etc The flag fProcessingSolid will be false for the last case The possibility of any or all of these three scenarios occurring for both permanent and transient objects affects the implementation of a scene handler if there is any attempt to build a graphical database This is reflected in the templates XXXStored and XXXSG described in Section 3 5 1 1 1 Transients are discussed in Section 3 5 1 6 G4TrajectoriesModel At end of event the trajectory container is unpacked and
39. ds For specific solids the G4PhysicalVolumeModel that provides the solids also provides via PreAddSolid a pointer to its vis attributes If the vis attribites pointer in the logical volume is zero it provides a pointer to the default vis attributes in the model which in turn is currently provided by the viewer s vis attributes see G4VSceneHandler CreateModelingParameters So the vis attributes pointer is guaranteed to be pertinent If the concrete driver does not implement AddSolid for any particular solid the base class converts it to primitives usually a G4Polyhedron and again the vis attributes pointer is guaranteed 2 12 6 1 4 Drawing style The drawing style is normally determined by the view parameters but for individual drawable ob jects it may be overridden by the forced drawing style flags in the vis attributes A utility function G4ViewParameters DrawingStyle G4VSceneHandler GetDrawingStyle is provided G4ViewParameters DrawingStyle drawing style GetDrawingStyle pVisAtts 2 12 6 1 5 Auxiliary edges Similarly the visibility of auxiliary soft edges is normally determined by the view parameters but may be overridden by the forced auxiliary edge visible flag in the vis attributes Again a utility function G4VSceneHandler GetAuxEdge Visible is provided G4bool isAuxEdgeVisible GetAuxEdgeVisible pVisAtts 2 12 6 1 6 LineSegmentsPerCircle Also the precision of rendering curved edges in the polyhedral rep
40. e Reference Manual which provides a list of Geant4 classes and their major methods Detailed discussions of the physics included in Geant4 are provided in the Physics Reference Manual 1 2 How to use this manual Part I to understand the goal of the software design of Geant4 it is useful to begin by reading the User Require ments Document referred to in the next section Part II Design and Function of the Geant4 Categories provides detailed information about the design of each class category and the classes in it Before considering an extension of one of the toolkit categories a detailed understanding of that category is required Part III Extending Toolkit Functionality explains in some detail how to extend the functionality of Geant4 Most of the class categories are covered and some which are especially useful to most users are covered in greater detail Itis not necessary to understand the entire manual before adding a new functionality To add a new physics process for example only the following items must be read and understood e the design principle described in the Physics processes chapter of Part II e techniques explained in the Physics processes chapter of Part III 1 3 User Requirements Document At the beginning of Geant4 development a set of user requirements was collected in order to inform the object oriented analysis and design of the toolkit The User Requirements Document follow
41. e approach to the particle tracking design would be to integrate all functionalities required for the propagation of a particle into a single class This design approach looks object oriented because a particle in the real world propagates by itself while interacting with the material surrounding it However in terms of data hiding which is one of the most important ingredients in the object oriented approach the design can be improved Combining all the necessary functionalities into a single class exposes all the data attributes to a large number of methods in the class This is basically equivalent to using a common block in Fortran Instead of the big class approach a hierarchical design was employed by Geant4 The hierarchical approach which includes inheritance and aggregation enables large complex software systems to be designed in a structured way The simulation of a particle passing through matter is a complex task involving particles detector geometry physics interactions and hits in the detector It is well suited to the hierarchical approach The hierarchical design manages the complexity of the tracking category by separating the system into layers Each layer may then be designed independently of the others In order to maintain high performance tracking use of the inheritance is a relation hierarchy in the tracking category was avoided as much as possible For example t rack and particle classes might have been designed so
42. e by overriding the G4VisManager RegisterModelFactory method in a subclass See for example the G4VisManager implementa tion G4VisExecutive RegisterModelFactories RegisterModelFactory new G4TrajectoryDrawByParticlelDFactory 3 5 3 Trajectory Filtering 3 5 3 1 Creating a new trajectory filter model New trajectory filters must inherit at least from G4VFilter The models supplied with the Geant4 distribution inherit from G4SmartFilter which implements some specialisations on top of G4VFilter The models implement these pure virtual functions 49 Extending Toolkit Functionality Evaluate method implemented in subclass virtual G4bool Evaluate const T amp 0 Print subclass configuration virtual void Print std ostream amp ostr const 0 To use the new filter model directly in compiled code simply register it with the G4VisManager eg G4VisManager visManager new G4VisExecutive visManager gt Initialise Create custom model MyCustomTrajectoryFilterModel myModel new MyCustomTrajectoryFilterModel custom Configure it if necessary then register with G4VisManager visManager gt RegisterModel myModel 3 5 3 2 Adding interactive functionality Additional classes need to be written if the new model is to be created and configured interactively The mechanism is exactly the same as that used to create enchanced trajectory drawing models and associated messengers See the fil
43. e virtual function virtual ModelAndMessengers Create const G4String amp placement const G4String amp modelName 0 23 where placement indicates which directory space the commands should occupy See for example G4TrajectoryDrawB yParticlelDFactory Design and Function of Geant4 Categories 2 12 5 View parameters View parameters such as camera parameters drawing styles wireframe surface etc are held by G4ViewParameters Each viewer holds a view parameters object which can be changed interactively and a default object for use in the vis viewer reset command If a toolkit developer of Geant4 wants to add entries of view parameters he should add fields and methods to G4ViewParameters 2 12 6 Visualisation Attributes All drawable objects should have a method const G4VisAttributes GetVisAttributes const A drawable object might be e a visible i e inheriting G4Visible such as a polyhedron polyline circle etc note that text is a slightly special case see below or asolid whose vis attributes are held in its logical volume 2 12 6 1 Finding the applicable vis attributes This is an issue for all scene handlers The scene handler is where the colour style auxiliary edge visibility marker size etc of individual drawable objects are needed 2 12 6 1 1 Visibles If the vis attributes pointer is zero drivers should pick up the default vis attributes from the viewer const G4VisAttributes
44. each model itself has an extent and a standard target point these are used to define the standard view see below In addition the scene keeps flags which indicate whether end of event objects should be accumulated or refreshed for each event or run e G4VGraphicsSystem This is an abstract base class for scene handler and viewer factories It is used by the visualisation manager to create scene handlers and viewers on request e G4VSceneHandler A sub class of G4VGraphicsScene itself an abstract base class for specific scene han dlers whose job is to convert the scene into graphics system specific code for the viewer For example the scene handler may create a graphical database taking care to separate run duration persistent and end of event transient information this is described further in Section 3 5 1 6 e G4VViewer An abstract base class for specific viewers Its job is to create windows or files and identify where and how the final view should be rendered It has view parameters G4ViewParameters which specify view point direction type of rendering wireframe or surface etc It is the view s responsibility noting the scene s extent and target point to choose a camera position and magnification that ensures that the scene is automati cally and comfortably rendered in the viewing window This is then the standard view and any further oper ations requested by the user zoom pan etc are relative to this standard view
45. ection data set classes are derived from the abstract class G4VCrossSection DataSet which declares methods that allow the process inquire about the applicability of an individual data set through IsApplicable const G4DynamicParticle const G4Element and to delegate the calculation of the actual cross section value through GetCrossSection const G4DynamicParticle const G4Element Final state production The G4HadronicInteraction base class is provided for final state generation It declares a minimal inter face of only one pure virtual method G4VParticleChange ApplyYourself const G4Track G4Nucleus amp G4HadronicProcess provides a registry for final state production models inheriting from G4Hadronic Interaction Again final state production model is meant in very general terms This can be an implementation of a quark gluon string model QGSM a sampling code for ENDF B data formats ENDFForm or a parametrisation describing only neutron elastic scattering off Silicon up to 300 MeV Isotope production For isotope production a base class G4VIsotope Production is provided It declares a method G4IsoResult GetIsotope const G4Track const G4Nucleus amp that calculates and returns the isotope production information Any concrete isotope production model will inherit from this class and implement the method Again the modeling possibilities are not limited and the implementation of concrete production model
46. ed on the command line the equivalent of vis viewer update vis scene notifyHandlers is also invoked after a change of scene vis scene add etc 3 5 1 3 What happens in DrawView This depends on the viewer Those with their own graphical database for example OpenGL s display lists or Open Inventor s scene graph do not need to re traverse the scene unless there has been a significant change of view parameters For example a mere change of viewpoint requires only a change of model view matrix whilst a change of rendering mode from wireframe to surface might require a rebuild of the graphical database A rebuild of the run duration persistent objects in the scene is called a kernel visit the viewer prints Traversing scene data Note that end of event transient objects are only rebuilt at the end of an event or run under control of the visu alisation manager Smart scene handlers keep them in separate display lists so that they can be rebuilt separately from the run duration objects see Section 3 5 1 6 Integrated viewers with no graphical database For example G4OpenGLImmediateXViewer DrawView NeedKernelVisit Always need to visit G4 kernel ProcessView FinishView Integrated viewers with graphical database For example G4OpenGLStoredXViewer DrawView KernelVisitDecision Private function containing if significant change of view parameters NeedKernelVisit ProcessView Fin
47. eer Et Rr teer erp MEINER 24 2 12 6 Visualisation Attributes item tret erp Eme RO ses E EE Ere inten 24 213 INtencoms MIC E 26 2 13 1 Design Philosophy cir erigere FRE RERO Ainas escri 26 2 132 Cl ss DeSIgn iii eR dit 26 3 Extending Toolkit Functionality 15 5 rete ette ae pea ce Rex tore ret e pe IE ER ER EE 28 3 1 Geometry eR PE EE RE NISI IP P SERT 28 3 1 1 What can be extended open remi Cer ED Per rrr cr 28 3 1 2 Adding a new type of Solid emen men menter 28 3 1 3 Modifying the Navigator eet m ERR e ERR RR EATUR PUE ER BER ER ER caos 31 3 2 Electromagnetic Fields 5 m eee oet bet Pee epe eee ee ee teer aes eh ER 31 32 1 Creating a New Type of Field sci sc eed err HE eed 31 Geant4 User s Guide for Toolkit Developers 3 3 Physi s PROCESSES siosio eskea EE EU erp ES 34 3 4 adronic PHYSICS 2 eto Gee rt er letters 34 3 41 Imtrod ction 42 dete ve e Gas Win eto t eet ta dots 34 3 42 Principal Considerations rer eto rte REP podrias 34 3 4 3 Level 1 Framework processes sss eee ee rene 34 3 4 4 Level 2 Framework Cross Sections and Models ooocoocccncccncccnccnncnncconccnnccnnccnnccnncons 35 3 4 5 Level 3 Framework Theoretical Models esseeeHH 38 3 4 6 Level 4 Frameworks String Parton Models and Intra Nuclear Cascade 40 3 4 7 Level 5 Framework String De excitation sese HH 41 3 3 Visualisation i
48. ei ce pro bentuaceeestea ses EORR ABO par ED SE ERE AE PEOR esha P IE daa eats 42 3 5 1 Creating a new graphics driver mem ementi 42 3 52 Enhanced Trajectory Drawing lt 1 sssss3ss 3ssessssosncds ret ert Eee ER ERR SEE Eea EPRS dees 48 3 5 3 Trajectory Filtering n cise sconces tee shes ee HE eripe IE NERIS 49 3 544 Other R sources ceso rias Oe CE baec Pe e P ORDEI ET gehe o 50 Bibliography Liar E a AS I enne ener rem E EI 51 Chapter 1 Introduction 1 1 Scope of this manual The User s Guide for Toolkit Developers provides detailed information about the design of Geant4 classes as well as the information required to extend the current functionality of the Geant4 toolkit This manual is designed to e provide a repository of information for those who want to understand or refer to the detailed design of the toolkit and e provide details and procedures for extending the functionality of the toolkit so that experienced users may contribute code which is consistent with the overall design of Geant4 This manual is intended for developers and experienced users of Geant4 It is assumed that the reader is already familiar with functionality of the Geant4 toolkit as explained in the User s Guide For Application Developers and also has a working knowledge of programming using C A knowledge of object oriented analysis and design will also be useful in understanding this manual It is also useful to consult the Softwar
49. eometrical volumes compute the length a particle can travel from a point in a certain direction before encountering a volume boundary The Navigator utilises one helper class for each type of physical volume that exists You will have to reuse the helper classes provided in the base Navigator or create new ones for the new type of physical volume To extend G4Navigator you will have then to inherit from it and modify these functions in your ModifiedNavigator to request the answers for your new physical volume type from the new helper class The ModifiedNavigator should delegate other cases to the Geant4 s standard Navigator Replacing the Navigator Replacing the Navigator is another possible operation It is similar to extending the Navigator in that any types of physical volume that will be allowed must be handled by it The same functionality is required as described in the previous section However the amount of work is probably potentially larger if support for all the current types of physical volumes is required The Navigator utilises one helper class for each type of physical volume that exists These could also potentially be replaced allowing a simpler way to create a new navigation system 3 2 Electromagnetic Fields 3 2 1 Creating a New Type of Field Geant4 currently handles magnetic and electric fields and in future releases will handle combined electromagnetic fields Fields due to other forces not yet included in Gea
50. epresented by specialized physical volumes such as replicas and parameterized placements sometimes resulting in a large savings in memory In Geant4 the logical volume has been refined by defining the shape as a separate entity called a solid Solids with simple shapes like rectilinear boxes trapezoids spherical or cylindrical sections or shells each have their properties coded separately in accord with the concept of Constructed Solid Geometry CSG More complex solids are defined by their bounding surfaces which can be planes second order surfaces or higher order B spline surfaces and belong to the Boundary Representations BREP sub category Another way to build solids is by boolean combination union intersection and subtraction The elemental solids should be CSGs Although a detector is naturally and best described as by a hierarchy of volumes efficiency is not critically depen dent on this An optimization technique called voxelization allows efficient navigation even in flat geometries typical of those produced by CAD systems 2 7 2 Class Design e G4GeometryManager responsible for managing high level objects in the geometry subdomain notably including opening and closing locking the geometry and creating deleting optimization information for G4Navigator The class is a singleton Design and Function of Geant4 Categories G4LogicalVolumeStore a container for optionally storing created log
51. es collections of events that share a common beam and detector implementation 2 2 2 Class Design e G4Run This class represents a run An object of this class is constructed and deleted by G4RunManager e G4RunManager the run controller class Users must register detector construction physics list and primary generator action classes to it G RunManager or a derived class must be a singleton e G4RunManagerKernel provides control of the Geant4 kernel This class is constructed by G4RunManager Status of this chapter 28 06 05 under construction December 2006 Converted from latex to Docbook by K Amako 2 3 Event 2 3 1 Design Philosophy In high energy physics the primary unit of an experimental run is an event An event consists of a set of primary particles produced in an interaction and a set of detector responses to these particles In Geant4 objects of the G4Event class are the primary units of a simulation run Before the event is processed it contains primary vertices and primary particles produced by an external physics generator After the event is processed it may also contain hits digitizations and optionally trajectories generated by the simulation The event category manages events and provides an abstract interface to external physics generators G4Event and its content vertices and particles are independent of other classes This isolation allows Geant4 based simulation programs to be independent of specifi
52. esign of the generic physics process G4VProcess and its relation to the process manager is shown in Figure 2 4 Figure 2 5 shows how specific physics processes are related to G4VProcess GaPhysiceTable GaProcesz Vector GAPhysksL ng vt and others with arbitrary binning Figure 2 4 Management of Physics Processes G4VRestContincuousDiscrete G4VRestContinuous Process AlongStepDolt G4VProcess GetContinuousStepLimit AlongStepDoht t Doh a AlongStepGetPhrysicalinter tRestDok AffestGetPhysi P PosiStegGetPhysicalinteractioLengh T nLifeTime y e 4 GaVRestDiscreteFrocess GaVContnucusProcess GavDiscreteProcess GeiMeanFreePath PoxtStepDelt vw b GsemuttipieScatenng G4ComptonScattenng Dolt Ganionisation G4eplusAnnihitation G4Decay sportation D PastStepDo t ontinucusStepl imit GetMeanF reePath A Do Figure 2 5 Management of Physics Processes Status of this chapter 27 06 05 section on design philosophy added by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 6 Hits and Digitization 2 6 1 Design Philosophy In Geant4 a hit is a snapshot of a physical interaction or an accumulation of interactions of a track or tracks in a sensitive detector component A digitization or digit represents a detector output such as an ADC TDC count or a trigger signal A digit is created from one or more hits and or other
53. ew model care should be taken to handle the possibility that the G4ModelingParameters pointer is zero Currently the only use of the modeling parameters is to communicate the culling policy Most models therefore have no need for modeling parameters 3 5 2 Enhanced Trajectory Drawing 3 5 2 1 Creating a new trajectory model New trajectory models must inherit from G4VTrajectoryModel and implement these pure virtual functions virtual void Draw const G4VTrajectory amp G4int i mode 0 const G4bool amp visible true const 0 virtual void Print std ostream amp ostr const 0 To use the new model directly in compiled code simply register it with the G4 VisManager eg G4VisManager visManager new G4VisExecutive visManager gt Initialise Create custom model MyCustomTrajectoryModel myModel new MyCustomTrajectoryModel custom Configure it if necessary then register with G4VisManager Heise Gores REDEEM dC UM EE 3 5 2 2 Adding interactive functionality Additional classes need to be written if the new model is to be created and configured interactively Messenger classes Messengers to configure the model should inherit from G4VModelCommand The concrete trajectory model type should be used for the template parameter eg 48 Extending Toolkit Functionality class G4MyCustomModelCommand public G4VModelCommand lt G4TrajectoryDrawByParticleID gt y A number of general use templated com
54. gate takes as arguments a three dimensional model of a wounded nucleus and a set of secondaries with energies and positions The base class for pre equilibrium decay models GAVPre CompoundModel inherits from G4Hadronic Interaction again making any concrete implementation usable as stand alone model It adds a pure virtual DeExcite method for further evolution of the system when intra nuclear transport assumptions break down DeExcite takes a G4Fragment the Geant4 representation of an excited nucleus as argument The base class for evaporation phases GAVExcitation Handler declares an abstract method BreakIt UP for compound decay Framework functionality The G4TheoFSGenerator class inherits from G4Hadronic Interaction and hence can be regis tered as a model for final state production with a hadronic process It allows a concrete implementation of G4VIntranuclear TransportModel and G4VHighEnergy Generator to be registered and dele gates initial interactions and intra nuclear transport of the corresponding secondaries to the respective classes The design is a complex variant of a Strategy The most spectacular application of this pattern is the use of parton string models for string excitation quark molecular dynamics for correlated string decay and quantum molecular dynamics for transport a combination which promises to result in a coherent description of quark gluon plasma in high energy nucleus nucleus interactions
55. gure 3 2 for the cross section aspects Figure 3 3 for the final state production aspects and figure Figure 3 4 for the isotope production aspects ecAbstatt gt G4HadronicProcess Pcovitual gt gt GetMicroscopicCrassSectionr tes 1StepOo ki peP reductioninia XcpaProductionModal EnabletsoigpeProductionG tally P e Concratess ceConagig lt lt Concretes gt lt lt Cancrata gt gt G4HadronFissionProcess G4HadroninelasticProcess G4HadronElasticProcess G4HadronCaptureProcess I ji it lt lt Concrete gt gt lt G4CrossSectionDataStore MaciiDataSat aetCrosssactien cConcretess 30 ADataSet lt lt Puraly Abstracts pret G4VCrossSectionDataSet 1 Applicable HaaicicssSaction Cancretes BDataSet Figure 3 2 Level 2 implementation framework of the hadronic category of Geant4 cross section aspect Abstract G4HadronicProcess lt lt virtual gt gt GetMicroscopicCrossSection lt lt virtual gt gt PostStepDolt VregisterMe ChooseHadronicinteraction GeneralPostStep Dolt lt lt static gt gt GetleotopeProductionInfo tRegisterlsotepe PreductionModel lt lt static gt gt EnablelsotopeProductionGlobally lt lt static gt gt DisablelsotopeProductionGlobally VEnablelsotopeCounting WDisablelsotopeCounting lt lt Concrete gt gt 0 4 G4EnergyRangeManager SONIS 1 S4HadronicInteraction o
56. h all categories without being perturbed by the dependencies among classes The capturing of commands is handled by a C abstract class G4UIsession Various concrete implementations of the command capturer are contained in the user interfaces category Taking into account the rapid evolution of graphical user interface GUI technology and consequent dependence on external facilities plural and extensible GUIs are offered Programmers need only know how to register the commands and parameters appropriate to their problem domain no knowledge of GUI programming is required to allow an application to use them through one of the available GUIs The intercoms category also provides the virtual base classes e G4VVisManager e G4VGraphicsScene and e G4VGlobalFastSimulationManager 2 13 2 Class Design e Gd4UlSession e G4UIBatch G4UICommand e G4UIparameter e G4UImessenger The object oriented design of the user interface related classes is shown in the class diagram Figure 2 21 The diagram is described in the Booch notation GaUlm Gat GaUltcl ethods o be writen by the Figure 2 21 Overview of intercom classes Status of this chapter 27 06 05 design philosophy from Geant4 general paper and class design sections added by D H Wright 26 Design and Function of Geant4 Categories Dec 2006 Conversion from latex to Docbook verson by K Amako 27 Chapter 3 Extending Toolkit Fu
57. his point in time the usage of the G4VFragmentation Function is not enforced by design but made available from the G4VSt ring Fragmentation to an implementer of a concrete string decay G4VSt ring Fragment ation provides a registering mechanism for the concrete fragmentation function It delegates the calculation of zf of the hadron to split of the string to the concrete implementation Standardisation in this area is expected 3 5 Visualisation This Chapter is intended to be read after Chapter Section 2 12 on Visualisation object oriented design in Part II Many of the concepts used here are defined there and it strongly recommended that a writer of a new visualisation driver or trajectory drawer reads Chapter Section 2 12 first The class structure described there is summarised in Figure 3 9 G4VVismanager G4VGraphicsScene Graphics Interface G4VisManager G4VGraphicsSystem G4VSceneHandler G4VViewer G4VisExecutive GAXXX G4xxxSceneHandler GAXXXViewer Geant4 Visualisation System G4Scene G4ViewParameters Figure 3 9 Geant Visualisation System Class Diagram 3 5 1 Creating a new graphics driver To create a new graphics driver for Geant4 it is necessary to implement a new set of three classes derived from the three base classes G4VGraphicsSystem G4VSceneHandler and G4VViewer 3 5 1 1 A useful place to start A skeleton set of classes is included in the code distribution
58. hods from the following books e B H Flowers An introduction to Numerical Methods In C Claredon Press Oxford 1995 e M Abramowitz I Stegun Handbook of mathematical functions DOVER Publications INC New York 1965 chapters 9 10 and 22 HEPGeometry Documentation for the HEPGeometry module is provided in the CLHEP Reference Guide http cern ch clhep manual RefGuide or the CLHEP User Manual http cern ch clhep manual UserGuide Status of this chapter 01 12 02 minor update by G Cosmo 20 Design and Function of Geant4 Categories 18 06 05 introductory paragraphs added and minor grammar changes by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 12 Visualisation 2 12 1 Design Philosophy The visualisation category consists of the classes required to display detector geometry particle trajectories track ing steps and hits It also provides visualisation drivers which are interfaces to external graphics systems A wide variety of user requirements went into the design of the visualisation category for example e very quick response in surveying successive events high quality output for presentation and documentation flexible camera control for debugging detector geometry and physics e Selection of visualisable objects interactive picking of graphical objects for attribute editing or feedback to the associated data highlighting incorrect intersections of physi
59. i l irom Globals SA G4DecayProducts me G4DecayChannel ui Dr a GetParentParticke ABR Vector RWTPtrSor Boost GetParenti pe tedVector eren Seagal 9 hom RWTook J 1 Y poe Seen b F 1 G4DecayProducts 1 ListElement G4MuonDecayChannel y next G4 DecayProductsListEl rment 0 a E gt reru ad G4Decay gt F rom PhysicsProcess LI Decay Taai eara and many others ThreeBodyDecaylti ManyBodyDecaylii Figure 2 15 Particle Decay Table Status of this chapter 27 06 05 section on design philosophy added from Geant4 general paper by D H Wright 16 Design and Function of Geant4 Categories Dec 2006 Conversion from latex to Docbook verson by K Amako 2 10 Materials 2 10 1 Design Philosophy The design of the materials category reflects what exists in nature materials are made of a single element or a mixture of elements and elements are made of a single isotope or a mixture of isotopes Because the physical properties of materials can be described in a generic way by quantities which can be specified directly such as density or derived from the element composition only concrete classes are necessary in this category The material category implements the facilities necessary to describe the physical properties of materials for the simulation of particle matter interactions Characteristics like radiation and interaction length excitation energy loss coefficie
60. ical volumes It enables traversal of all logical volumes by the Ul user etc G4LogicalVolume represents a leaf node or unpositioned subtree in the geometry hierarchy It may have daughters ascribed to it and is also responsible for retrieval of the physical and tracking attributes of the physical volume that it represents These attributes include solid material magnetic field and optionally user limits sensitive detectors etc Logical volumes are optionally entered into the G4LogicalVolumeStore G4MagneticField a class responsible for the magnetic field in each volume including the calculation of particle trajectories along curved paths In cases where the geometry step limits the particle s step the distance calculated is guaranteed to be the distance to a volume boundary G4Navigator a class used by the tracking management able to obtain calculate tracking time geometrical information such as distance to the next volume or to find the physical volume containing a given point in the world reference system The navigator maintains a transformation history and other information used to optimize the tracking time performance G4NavigationHistory responsible for maintenance of the history of the path taken through the geometrical hierarchy It is principally a utility class for use by G4Navigator G4NormalNavigation a utility class for navigation in volumes containing only G4PVPlacement daughter volumes G4ParameterisedNavigation a u
61. icitly specifying an engine which can be shared by many distribution objects The static interface is skipped here localEngine 1 flat gt A flat a Mete Mt A d flat 5 flat PoissonDi z ME stribution 8 fire gt lt 2 fira fi are g SN FlatDistrib O re e fire 7 Bwoistribu ution i SN tion ExpDistrib GaussDist ution ribution Figure 2 19 Shooting via distribution objects Figure 2 20 illustrates the situation when many generators are defined each by a distribution and an engine The static interface is skipped here E ngi nes tft ow E eo Nat 4 A 7 flat 0 10 shoot E a sati gt PoissonDi fens stribution E 2 shoot uina E el m FlatDistrib T ar a Das BWDistrib ution a ution ExpDistrib GaussDist ution ribution Figure 2 20 Shooting with arbitrary engines For detailed documentation about the HEPRandom classes see the CLHEP Reference Guide http cern ch clhep manual RefGuide or the CLHEP User Manua http cern ch clhep manual UserGuide Informations written in this manual are extracted from the original manifesto distributed with the HEPRandom package http cern ch clhep manual UserGuide Random Random html HEPNumerics The HEPNumerics module includes a set of classes which implement numerical algorithms for general use in Geant4 The User s Guide for Application Developers contains a description of each class Most of the algorithms were implemented using met
62. implementation can represent both these extreme cases GAVRestDiscrete Process Each of these classes declares two types of methods one for calculating the time to interaction or the physical interaction length allowing tracking to request the information necessary to decide on the process responsible for final state production and one to compute the final state These are pure virtual methods and have to be implemented in each individual derived class as enforced by the compiler Framework functionality The functionality provided is through the use of process base class pointers in the tracking physics interface and the G4Process Manager All functionality is implemented in abstract and registration of derived process classes with the GAProcess Manager of an individual particle allows for arbitrary combination of both Geant4 provided processes and user implemented processes This registration mechanism is a modification on a Chain of Responsibility It is outside the scope of the current paper and its description is available from G4Manual 3 4 4 Level 2 Framework Cross Sections and Models Atthe next level of abstraction only processes that occur for particles in flight are considered For these it is easily Observed that the sources of cross sections and final state production are rarely the same Also different sources will come with different restrictions The principal use cases of the framework are addressing these commonalitie
63. in maximum allowed Step in the volume define by the user through G4UserLimits The PostStepGetPhysicalInteractionLength of all active processes is called Each process returns a step length and the minimum one is chosen This method also returns a G4ForceCondition flag to indicate if the process is forced or not Forced Corresponding PostStepDolt is forced NotForced Corresponding PostStepDolt is not forced unless this process limits the step Conditionally Only when AlongStepDolt limits the step cor responding PoststepDolt is invoked ExclusivelyForced Corresponding PostStepDolt is exclusively forced All other Dolt including AlongStepDolts are ignored The AlongStepGetPhysicalInteractionLength method of all active processes is called Each process returns a step length and the minimum of these and the This method also returns a fGPILSelection flag to indicate if the process is the selected one can be is forced or not CandidateForSelection this process can be the winner If its step length is the smallest it will be the process defining the step the process NotCandidateForSelection this process cannot be the winner Even if its step length is taken as the smallest it will not be the process defining the step The method G4SteppingManager InvokeAlongStepDolts is in charge of calling the AlongStep Dolt methods of the different processes If the current step is defined by a ExclusivelyForced PostStepGetPhysicalInteractio
64. ion of Geant4 Categories G4DAWNFILEView public G4V View for rendering 3D scenes Several visualisation drivers are distributed with Geant4 They are complementary to each other in many aspects For details see Chapter 8 of the User s Guide for Application Developers 2 12 4 Modeling sub category G4VModel a base class for visualisation models A model is a graphics system independent description of a Geant4 component The sub category visualisation modeling defines how to model a 3D scene for visualisation The term 3D scene indicates a set of visualisable component objects put in a 3D world A concrete class inheriting from the abstract base class G4VModel defines a model which describes how to visualise the corresponding component object belonging to a 3D scene G4ModelingParameters defines various associated parameters For example G4PhysicalVolumeModel knows how to visualise a physical volume It describes a physical volume and its daughters to any desired depth G4HitsModel knows how to visualise hits G4TrajectoriesModel knows how to visualise trajectories The main task of a model is to describe itself to a 3D scene by giving a concrete implementation of the following virtual method of G4VModel virtual void DescribeYourselfTo G4VGraphicsScene amp 0 The argument class G4VGraphicsScene is a minimal abstract interface of a 3D scene for the Geant4 kernel defined in the graphics_reps category Since G4VSceneHandler and i
65. is to the exciton model The exciton model will take the information provided and calculate transitions and emissions until the number of excitons in the system equals the mean number of excitons expected in equilibrium for the current excitation energy Then it hands over to the evaporation phase The evaporation phase decays the residual nucleus and the Chain of Command rolls back to GATheoFS Generator accumulating the information produced in the various levels of delegation 3 4 6 Level 4 Frameworks String Parton Models and Intra Nuclear Cascade lt lt Abstract gt gt GaVPartonStringModel Puraly Abstracts gt ER k A gtWour uckus mun GaVStringFragmertation E d erii E gt GaEscitedSting Arragmertstringi 1 y eeeituals GetStrings L FcomeciHadranMo mentar geetTrisPointar Concrete lt lt Cancietes gt GstQuarkGluorStringModel aasin GatWourdedNuckus CrameD MractheString dorama Sting Crates al G4PythiaFragmentationinterface dI MES GAFTFMadel Concrete GaLongtudinalStringDecay oParticipants E n xs String GaussianPt afrchncesaxi Figure 3 6 Level 4 implementation framework of the hadronic category of Geant4 parton string aspect lt lt Puraly Abstracts G4VIntraNuclearTransportModel Sapplyvcursal G4VKineticNucieon PPropagater Dacay 5 Get Mamantum GaDelintion GatPostticnr G4V3D Nucleus A Piney T CENE asientos A Go
66. ishView e File writing viewers For example GADAWNFILEViewer DrawView NeedKernelVisit ProcessView Note that viewers needing to invoke FinishView must do it in DrawView 44 Extending Toolkit Functionality 3 5 1 4 What happens in ProcessView ProcessView is inherited from G4VViewer void G4VViewer ProcessView If ClearStore has been requested e g if the scene has changed of if the concrete viewer has decided that it necessary to visit the kernel perhaps because the view parameters have changed drastically this should be done in the concrete viewer s DrawView if fNeedKernelVisit fSceneHandler ProcessScene this fNeedKernelVisit false 3 5 1 5 What happens in ProcessScene ProcessScene is inherited from G4VSceneHandler It causes a traversal of the run duration models in the scene For drivers with graphical databases it causes a rebuild ClearStore Then for the run duration models fReadyForTransients false BeginModeling for each run duration model pModel DescribeYourselfTo this EndModeling fReadyForTransients true A second pass is made on request see G4VSceneHandler ProcessScene The use of fReadyFor Transients is described in Section 3 5 1 6 What happens then depends on the type of model G4AxesModel G4AxesModel DescribeYourselfTo simply calls sceneHandler AddPrimitive methods directly SceneHandler BeginPri
67. maintains the association between a solid and its net resultant local to global transform e G4GRSVolume object representing a touchable detector element It maintains associations between a phys ical volume and its net resultant local to global transform G4TransformStore a container for optionally storing created G4AffineTransform objects It is responsible for storing and providing access to transformations that are constant at tracking time e G4AffineTransform a class for geometric affine transformations It supports efficient arbitrary rotation and transformation of vectors and the computation of compound and inverse transformations A rotation flag is maintained internally for greater computational efficiency for transforms that do not involve rotation e G4UserLimits responsible for user limits on step size ascribable to individual volumes Figure 2 9 shows a general overview in UML notation of the geometry design A detailed collection of class diagrams from the geometry category is found in the Appendix Figure 2 9 Overview of the geometry 2 7 3 Additional Geometry Diagrams Additional diagrams for the object oriented design of the geometry related classes are included here Figure 2 10 shows the class diagram for smart voxels Figure 2 11 shows the class diagram for the navigator 13 Design and Function of Geant4 Categories Voze Header is passed D Gi oxelLimits during eesteactson to p
68. mands are available in G4ModelCommandsT hh e Factory class A factory class responsible for the model and associated messenger creation must also be written The factory should inherit from G4VModelFactory The abstract model type should be used for the template parameter eg class G4TrajectoryDrawByChargeFactory public G4VModelFactory lt G4VTrajectoryModel gt y The model and associated messengers should be constructed in the Create method Optionally a context object can also be created with its own associated messengers For example ModelAndMessengers G4TrajectoryDrawByParticlelDFactory Create const G4String amp placement const G4String amp name Create default context and model G4VisTrajContext context new G4VisTrajContext default G4TrajectoryDrawByParticleID model new G4TrajectoryDrawByParticleID name context Create messengers for default context configuration AddContextMsgrs context messengers placement name Create messengers for drawer messengers push_back new G4ModelCmdSetStringColour GA4TrajectoryDrawByParticleID model placement messengers push back new G4ModelCmdSetDefaultColour G4TrajectoryDrawByParticleID model placement messengers push back new G4ModelCmdVerbose G4TrajectoryDrawByParticleID model placement return ModelAndMessengers model messengers The new factory must then be registered with the visualisation manager This should be don
69. method of G4SteppingManager e Append a trajectory point to the trajectory object if it is requested Post tracking user intervention process Destroy the trajectory if it was created Stepping in G4SteppingManager Initialize current step If particle is stopped get the minimum life time from all the at rest processes and invoke InvokeAtRestDolt Procs for the selected AtRest processes If particle is not stopped e Invoke DefinePhysicalStepLength that finds the minimum step length demanded by the active processes e Invoke InvokeAlongStepDoltProcs e Update current track properties by taking into account all changes by AlongStepDolt e Update the safety e Invoke PostStepDolt of the active discrete process e Update the track length Send G4Step information to Hit Dig if the volume is sensitive Invoke the user intervention process e Return the value of the StepStatus 2 4 4 Interaction with Physics Processes The interaction of the tracking category with the physics processes is done in two ways First each process can limit the step length through one of its three Get PhysicalInteractionLength methods AtRest AlongStep or PostStep Second for the selected processes the Dolt AtRest AlongStep or PostStep methods are invoked All this interaction is managed by the Stepping method of G4SteppingManager To calculate the step length the DefinePhysicalStepLength method is called The flow of this method is the following Obta
70. mitives sceneHandler AddPrimitive x axis etc SceneHandler EndPrimitives Most other models are like this except for the following e G4PhysicalVolumeModel The geometry is descended recursively culling policy is enacted and for each accepted and possibly clipped solid SceneHandler PreAddSolid theAT pVisAttribs pSol DescribeYourselfTo sceneHandler For example if pSol points to a G4Box gt G4Box DescribeYourselfTo G4VGraphicsScene amp scene scene AddSolid this SceneHandler PostAddSolid The scene handler may implement the virtual function AddSolid const G4Box amp or inherit void G4VSceneHandler AddSolid const G4Box amp box RequestPrimitives box RequestPrimitives converts the solid into primitives G4Polyhedron and invokes AddPrimi tive 45 Extending Toolkit Functionality BeginPrimitives fpObjectTransformation pPolyhedron solid GetPolyhedron AddPrimitive pPolyhedron EndPrimitives The resulting default sequence for a G4PhysicalVolumeModel is shown in Figure 3 10 DrawView ProcessView ProcessScene BeginModeling pModel gt DescribeYourselfTo this sceneHandler PreAddSolid theAT pVisAttribs pSol DescribeYourselfTo sceneHandler sceneHandler AddSolid this RequestPrimitives solid BeginPrimitives fpObjectTransformation gt pPolyhedron solid GetPolyhe
71. nLength no AlongStep Dolt method will be invoked Else all the active continuous processes will be invoked and they return the ParticleChange After it for each process the following is executed e Update the G4Step information by using final state information of the track given by a physics process This is done through the UpdateStepForAlongStep method of the ParticleChange 6 Design and Function of Geant4 Categories e Then for each secondary e tis checked if its kinetic energy is smaller than the energy threshold for the material In this case the particle is assigned a 0 kinetic energy and its energy is added as deposited energy of the parent track This check is only done if the flag ApplyCutFlag is set for the particle by default it is set to false for all particles user may change it in its G4VUserPhysicsList If the track has the flag IsGoodForTracking true this check will have no effect used mainly to track particles below threshold e The parentID and the process pointer which created this track are set e The secondary track is added to the list of secondaries If it has O kinetic energy it is only added if it it invokes a rest process at the beginning of the tracking e The track status is set according to what the process defined The method G4SteppingManager InvokePostStepDolts is on charge of calling the PostStepDolt methods of the different processes Invoke the PostStepDolt methods of the specified di
72. nctionality 3 1 Geometry 3 1 1 What can be extended Geant4 already allows a user to describe any desired solid and to use it in a detector description in some cases however the user may want or need to extend Geant4 s geometry One reason can be that some methods and types in the geometry are general and the user can utilise specialised knowledge about his or her geometry to gain a speedup The most evident case where this can happen is when a particular type of solid is a key element for a specific detector geometry and an investment in improving its runtime performance may be worthwhile To extend the functionality of the Geometry in this way a toolkit developer must write a small number of methods for the new solid We will document below these methods and their specifications Note that the implementation details for some methods are not a trivial matter these methods must provide the functionality of finding whether a point is inside a solid finding the intersection of a line with it and finding the distance to the solid along any direction However once the solid class has been created with all its specifications fulfilled it can be used like any Geant4 solid as it implements the abstract interface of G4VSolid Other additions can also potentially be achieved For example an advanced user could add a new way of creating physical volumes However because each type of volume has a corresponding navigator helper this would require t
73. nerator getTheSeed get TheSeeds gellheTableSeeds selTheEngine seiTheSeed setTheSeeck I RandFlat fire a fireArray 4 RandPoisson firelnt fire shoat shoot shootarnyt shootrrayi shootinti fireArrayt o n 0 n SI RandGauss A RandExponential fired zs shcot RandBreitWigner shoot shoctAray lire fireArray shoot shactAray 10 n shoct rrayt firedrray fireArayt 0 nf 10 0 Figure 2 17 HEPRandom module Figure 2 18 is a dynamic object diagram illustrating the situation when a single random number is thrown by the static generator according to one of the available distributions Only one engine is assumed to active at a time Just one of the following Random Engines at a time is active HepRandomEngine HepJamesRandom default DRand48Engine RandEngine RanluxEngine RanecuEngine 4 E 2 setSuod long rt 1 sotTheEnghe theEngine RandGauss 4n thaGenarator 7 Mat de a 0n RandBreit gain f Th Sif sil X Wigner 5 shoot A aGenerator 16 n 107 6 HepRandom AT 15 flat Smp a RandPoisson ee 8 shoot 4 uj 14 shoot 12 fa 9 nai a RandExpon 1 sheot RandFlat d Figure 2 18 Shooting via the generator 19 Design and Function of Geant4 Categories Figure 2 19 illustrates a random number being thrown by expl
74. ng between a single value and an Ntuple The object oriented design of the hit related classes is shown in the following class diagrams The diagrams are described in the Booch notation Figure 2 6 shows the general management of hit classes Figure 2 7 shows the OO design of user related hit classes Figure 2 8 shows the OO design of the readout geometry GSDManager G4EventManage r 1 G4SDmessenger 4 manager a G4Vi Cmn a get hom EventManageme 9 G4Event ger P X irom Intercom pre nii 4 MteminateCurrent vert G4HCtableEi i P G4SteppingMan nent tresTop ager T H s from Tracking 1 1 G4sDStructure ice G LogicalVolume manager G4HCofThisEvent trom Geometry e 1 detector SensitiveQetector G4Step trom Tracking G4VHitsCollection 1 SDname G4String 49 aGoltectien 7 SDpathName GaSting collectionName GaString e G4VReadOut Geometry G4VHit ton diaw Print Y processHits A Figure 2 6 Overview of hit classes management e sCellection Hr VE a cabbimetertisCole tionArray Gat s calorimeter y craw tsColecion dii e RW Taria shakkar calorimeter calorimeterHii s t Ag chamberHits Colecti chamberi irigirs aera onArray D GaAllocalcr PWT PtiOrderedVe rom Globais or from Rogowa CcourterHitsCollection courterHitsCallectio d 1 Array 9 73 E counter courterHit Figure 2
75. nic show er simulation It is refined for more specific use cases by implementing a hierarchy of implementation frameworks each level implementing the common logic of a particular use case package in a concrete implementation of the interface specification of one framework level above this way refining the granularity of abstraction and delega tion This defines the Russian dolls architectural pattern Abstract classes are used as the delegation mechanism x All framework functional requirements were obtained through use case analysis In the following we present for each framework level the compressed use cases requirements designs including the flexibility provided and il lustrate the framework functionality with examples All design patterns cited are to be read as defined in Gam ma1995 3 4 3 Level 1 Framework processes There are two principal use cases of the level framework A user will want to choose the processes used for his particular simulation run and a physicist will want to write code for processes of his own and use these together with the rest of the system in a seamless manner Requirements 1 Provide a standard interface to be used by process implementations 2 Provide registration mechanisms for processes 1 The same can be achieved with template specialisations with slightly improved CPU performance but at the cost of significantly more complex designs and with present compilers significantly reduced port
76. nt geometrical entities They have only shape and encompass both CSG and boundary representations They are optionally entered into the G4SolidStore This class defines but does not Design and Function of Geant4 Categories implement functions to compute distances to from the shape Functions are also defined to check whether a point is inside the shape to return the surface normal of the shape at a given point and to compute the extent of the shape e G4VSweptSolid a solid created by performing a 3D transformation on a finite planar face e G4HalfSpaceSolid a solid created by the boolean AND of one or more half space surfaces G4BREPSolid a solid created by an abitrary set of finite surfaces e G4VTouchable a class that maintains a reference on a given touchable element of the detector a kind of bookmark It enables a given detector element to be saved during tracking in case of booleans user code etc and the corresponding G4PhysicalVolume retrieved later with its state information path through the tree optionally restored so that navigation can be restarted G4Touchables provide fast access to the transformation from the global reference system to that of the saved detector element e G4TouchableHistory object representing a touchable detector element and its history in the geomtrical hierarchy including its net resultant local gt global transform e GAGRSSolid object representing a touchable solid It
77. nt4 can be provided by describing the new field and the force it exerts on a particle passing through it For the time being all fields must be time independent This restriction may be lifted in the future In order to accommodate a new type of field two classes must be created a field type and a class that determines the force The Geant4 system must then be informed of the new field A new Field class A new type of Field class may be created by inheriting from G4Field class NewField public G4Field publie 31 Extending Toolkit Functionality void GetFieldValue const double Point 3 double pField 0 and deciding how many components your field will have and what each component represents For example three components are required to describe a vector field while only one component is required to describe a scalar field If you want your field to be a combination of different fields you must choose your convention for which field goes first which second etc For example to define an electromagnetic field we follow the convention that components 0 1 and 2 refer to the magnetic field and components 3 4 and 5 refer to the electric field By leaving the GetFieldValue method pure virtual you force those users who want to describe their field to create a class that implements it for their detector s instance of this field So documenting what each component means is required to give them the necessary information
78. ntation The base class for parton string models G4VParton String Model declares the Get Strings pure virtual method G4VSt ring Fragment ation the pure abstract base class for string fragmentation declares the interface for string fragmentation To fulfill the requirements on intra nuclear transport two abstract classes are provided G4V3DNucleus and G4VScatterer At this point in time the usage of these intra nuclear transport related classes by concrete codes is not enforced by designs as the details of the cascade loop are still model dependent and more experience has to be gathered to achieve standardisation It is within the responsibility of the implementers of concrete intra nuclear transport codes to use the abstract interfaces as defined in these classes The class diagram is shown in Figure 3 6 for the string parton model aspects and in Figure 3 7 for the intra nuclear transport Framework functionality Again variants of Strategy Bridge and Chain of Responsibility are used G4VParton StringModel imple ments the initialisation of a three dimensional model of a nucleus and the logic of scattering It delegates secondary production to string fragmentation through a G4VString Fragmentation pointer It provides a registering service for the concrete string fragmentation and delegates the string excitation to derived classes Selection of string excitation is through selection of derived class Selection of string fragmentation is
79. nts in the Bethe Bloch formula shell correction factors etc are computed from the element and if necessary the isotope composition The material category also implements facilities to describe surface properties used in the tracking of optical photons 2 10 2 Class Design The object oriented design of the materials related classes is shown in the class diagram Figure 2 16 The diagram is described in the Booch notation RWTPirOr deredVect om RWToolz 7 G4Material G4Element abe Table Tabia ij fii a UN s 1 1 A 1 1 iheMaterialTabl y nn ul iheElementTable thelsotope n s a n 1 bv n 18 G4Material Mate G4Element G4lsotope PddElement Addizotopet Dump Tablet ps Dump able ba e theElements thelsotopes i 1 e 1 G4Element Vector Sven 10 1 0 1 4 RWTPirVe ctor from RWToclz Figure 2 16 Status of this chapter 27 06 05 section on design philosophy add from Geant4 general paper by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 17 Design and Function of Geant4 Categories 2 11 Global Usage 2 11 1 Design Philosophy The global category covers the system of units constants numerics and random number handling It can be con sidered a place holder for general purpose classes used by all categories defined in Geant4 No back dependen cies to other Geant4 categories affect the global domain There are direct dependencies of the
80. o create a new Navigator as well To do this the user would have to inherit from G4Navigator and modify the new Navigator to handle this type of volumes This can certainly be done but will probably be made easier to achieve in the future versions of the Geant4 toolkit 3 1 2 Adding a new type of Solid We list below the required methods for integrating a new type of solid in Geant4 Note that Geant4 s specifica tions for a solid pay significant attention to what happens at points that are within a small distance tolerance kCarTolerance in the code of the surface So special care must be taken to handle these cases in considering all different possible scenarios in order to respect the specifications and allow the solid to be used correctly by the other components of the geometry module Creating a derived class of G4VSolid The solid must inherit from G4VSolid or one of its derived classes and implement its virtual functions Mandatory member functions you must define are the following pure virtual of G4VSolid EInside Inside const G4ThreeVector amp p G4double DistanceToIn const G4ThreeVector amp p G4double DistanceToIn const G4ThreeVector amp p const G4ThreeVector amp v G4ThreeVector SurfaceNormal const G4ThreeVector p G4double DistanceToOut const G4ThreeVector amp p G4double DistanceToOut const G4ThreeVector amp p const G4ThreeVector v const G4bool calcNorm false G4bool validNorm 0 G4ThreeVector n G4bool Calculate
81. ompletely fill the containing mother volume G4PV Parameterised a physical volume representing many touchable detector elements differing in their positioning and dimensions Both are calculated by means of a G4VParameterisation object Each element s position is calculated as per G4PVReplica and each element s shape can be modified by means of a user supplied formula G4VPVParameterisation a parameterisation class able to compute the transformation and indirectly the dimensions of parameterised volumes given a replication number G4SmartVoxelProxy a class for proxying smart voxels The class represents either a header in turn refering to more VoxelProxies or a node If created as a node calls to GetHeader cause an exception and likewise GetNode when a header G4SmartVoxelHeader represents a single axis of virtual division Contains the individual divisions which are potentially further divided along different axes G4SmartVoxelNode a single virtual division containing the physical volumes inside its boundaries and those of its parents G4VoxelLimits represents limitation restrictions of space where restrictions are only made perpendicular to the cartesian axes G4RotationMatrixStore a container for optionally storing created G4RotationMatrices G4SolidStore a container for optionally storing created solids It enables traversal of all any solids by the Ul user etc The class is a singleton G4VSolid position independe
82. oton and hadron interactions low energy providing alternative models extended down to lower energies than the standard package muons handling muon interactions e x rays providing specific code for x ray physics optical providing specific code for optical photons e utils collecting utility classes used by the above packages It provides the features of openness and extensibilty resulting from the use of object oriented technology alterna tive physics models obeying the same process abstract interface are often available for a given type of interaction For hadronic physics an additional set of implementation frameworks was added to accommodate the large num ber of possible modeling approaches The top level framework provides the basic interface to other Geant4 cate gories It satisfies the most general use case for hadronic shower simulations namely to provide inclusive cross sections and final state generation The frameworks are then refined for increasingly specific use cases building a hierarchy in which each level implements the interface specified by the level above it A given hadronic process Design and Function of Geant4 Categories may be implemented at any one of these levels For example the process may be implemented by one of several models and each of the models may in turn be implemented by several sub models at the lower framework levels 2 5 2 Class Design 2 5 2 1 General The object oriented d
83. r a batch job even if some code like the above is still included Most of the novice examples can be built this way if G4VIS_NONE is specified The concrete implementation of this interface is hereafter referred to as the visualisation manager e G4VGraphicsScene The visualisation manager must also provide a concrete implementation of the subsidiary interface G4VGraphicsScene It is only for use by the kernel and the modeling category It offers direct access to a scene handler through a reference provided by the visualisation manager It is described in more detail in the section on extending the toolkit functionality The Geant4 distribution includes implementations of the above interfaces namely G4VisManager and G4VSceneHandler respectively and their associated classes These define further abstract base classes for visu alisation drivers Together they form the Geant4 Visualisation System A variety of concrete visualisation drivers are also included in the distribution Details of how to implement a visualisation driver are given in Section 3 5 Of 21 Design and Function of Geant4 Categories course it is always possible for a user to implement his or her own concrete implementations of G4V VisManager and G4VGraphicsScene replacing the Geant4 Visualisation System altogether 2 12 3 The Geant4 Visualisation System The Geant4 Visualisation System consists of e G4VisManager An implementation of the G4VVisManager interface
84. rastructure for accessing and steering of isotope production information It allows to enable and disable the calculation of isotope production information globally or for individual processes and to retrieve the isotope production information through the G4IsoParticleChange GetIsotopeProductionInfo method at the end of each step The G4HadronicProcess is a finite state machine that will ensure the GetIsotope ProductionInfo re turns a non zero value only at the first call after isotope production occurred An example of the use of this func tionality is the study of activation of a Germanium detector in a high precision low background experiment 3 4 5 Level 3 Framework Theoretical Models rece G4TheoFSGenerator _ GiParton TrareportMadel GaVPreCompeundModel GaPythiaAhlrterlace GaVHighEnergyGererator rue Ae rosae Ga VExcitationHarxller G4VPartonStringModel dcan GaPythiaNhinterface GaHadronKinelicModel G40MDModel Gt HadronicCascade LL i jl jl Figure 3 5 Level 3 implementation framework of the hadronic category of Geant4 theoretical model aspect Geant4 provides at present one implementation framework for theory driven models The main use case is that of a user wishing to use theoretical models in general and to use various intra nuclear transport or pre compound models together with models simulating the initial interactions at very high energies Requirements 1
85. resentation of volumes is normally deter mined by the view parameters but may be overridden by a forced attribute A utility function that respects this G4VSceneHandler GetNoOfSides is provided For example G4Polyhedron SetNumberOfRotationSteps GetNoOfSides pVisAttribs 2 12 6 1 7 Marker size These have nothing to do with vis attributes they are an extra property of markers i e objects that inherit G4V Marker circles squares text etc However the algorithm for the actual size is quite complicated and a utility function G4VSceneHandler GetMarkerSize is provided MarkerSizeType sizeType G4double size GetMarkerSize text sizeType sizeType is world or screen signifying that the size is in world coordinates or screen coordinates respectively Status of this chapter 27 06 05 partially re organized and section on design philosophy added from Geant4 general paper by D H Wright 13 10 05 Section on vis attributes added by John Allison 25 Design and Function of Geant4 Categories 06 01 06 Re write of Design Philosphy and introduction of The Graphics Interfaces and The Geant4 Visu alisation System by John Allison Dec 2006 Conversion from latex to Docbook verson by K Amako 2 13 Intercoms 2 13 1 Design Philosophy The intercoms category implements an expandable command interpreter which is the key mechanism in Geant4 for realizing customizable and state dependent user interactions wit
86. rovide information on limits of any previous Figure 2 10 Class diagram for smart voxels classes tightly s tory Wick minister De Se composted trsnereenas ier and TTA favigatar makos Uam GE four Satliayr navigation coupled ta nat fed tr valune replicstien nunber Information gt GiNavigationHistory GetTopVoluneT Wewbevel L tnorma INav Vercelli 1 GaWornalNavigatidn AreplicaNas from navigatidn 1 f j a GiVoxe Navigation SConputest p Meveliocate ia ccconst gt gt BackLocate Scomputesatety Sccvirtual gt gt Comp ccvirtual gt gt Comp Secvirtual Leve loxe Locate Figure 2 11 Class diagram for the navigator Status of this chapter 27 06 05 subsection on design philosphy from Geant4 general paper added by D H Wright 2 8 Electromagnetic Fields The object oriented design of the classes related to the electromagnetic field is shown in the class diagram of Figure 2 12 The diagram is described in UML notation 14 Design and Function of Geant4 Categories Figure 2 12 Electromagnetic Field 2 9 Particles 2 9 1 Design Philosophy The particles category implements the facilities necessary to describe the physical properties of particles for the simulation of particle matter interactions All particles are based on the G4ParticleDefinition class which de scribes basic properties such as mass charge etc and also allo
87. s A user might want to combine different cross sections and final state or isotope production models as provided by Geant4 and a physicist might want to implement his own model for particular situation and add cross section data sets that are relevant for his particular analysis to the system in a seamless manner Requirements 1 Flexible choice of inclusive scattering cross sections 2 Ability to use different data sets for different parts of the simulation depending on the conditions at the point of interaction 35 Extending Toolkit Functionality 9 Ability to add user defined data sets in a seamless manner Flexible unconstrained choice of final state production models Ability to use different final state production codes for different parts of the simulation depending on the conditions at the point of interaction Ability to add user defined final state production models in a seamless manner Flexible choice of isotope production models to run in parasitic mode to any kind of transport models Ability to use different isotope production codes for different parts of the simulation depending on the con ditions at the point of interaction Ability to add user defined isotope production models in a seamless manner Design and interfaces The above requirements are implemented in three framework components one for cross sections final state pro duction and isotope production each The class diagrams are shown in Fi
88. s is not restricted in any way By convention the Get Isotope method returns NULL if the model is not applicable for the current projectile target combination Framework functionality Cross Sections G4HadronicProcess provides registering possibilities for data sets A default is provided covering all possible conditions to some approximation The process stores and retrieves the data sets through a data store that acts like a FILO stack a Chain of Responsibility with a First In Last Out decision strategy This allows the user to 37 Extending Toolkit Functionality map out the entire parameter space by overlaying cross section data sets to optimise the overall result Examples are the cross sections for low energy neutron transport If these are registered last by the user they will be used whenever low energy neutrons are encountered In all other conditions the system falls back on the default or data sets with earlier registration dates The fact that the registration is done through abstract base classes with no side effects allows the user to implement and use his own cross sections Examples are special reaction cross sections of nuclear interactions that might be used for analysis at LHC to control the systematic error Final state production The G4HadronicProcess class provides a registration service for classes deriving from G4Hadronic In teraction and delegates final state production to the applicable model G
89. s the PSS 05 software engi neering standards and is available at http cern ch geant4 OOAandD URD pdf This document provides a general description of the main capabilities and constraints of the toolkit It also defines three types of users characterized by their level of interaction with the system Specific requirements are also listed and classified Status of this chapter 24 06 05 re organized and re written by D H Wright Chapter 2 Design and Function of Geant4 Categories 2 1 Introduction Geant4 exploits advanced software engineering techniques based on the Booch UML Object Oriented Method ology and follows the evolution of the ESA Software Engineering Standards for the development process The spiral or iterative approach has been adopted User requirements were collected in the initial phase and problem domain decomposition object oriented methods and CASE tools were used for analysis and design This pro duced a clear hierarchical structure of sub domains linked by a uni directional flow of dependencies This led to a software product which is modular and flexible a toolkit and in which the physics implementation is transparent and open to user validation of physics predictions It allows the user to understand customize and extend the toolkit in all domains At the same time the modular architecture allows the user to load only needed components 2 2 Run 2 2 1 Design Philosophy The run category manag
90. screte process the one selected by the PostStepGetPhys icalInteractionLength and they return the ParticleChange The order of invocation of processes is inverse to the order used for the GPIL methods After it for each process the following is executed e Update PostStepPoint of Step according to ParticleChange e Update G4Track according to ParticleChange after each PostStepDolt e Update safety after each invocation of PostStepDolts e The secondaries from ParticleChange are stored to SecondaryList Then for each secondary e Itis checked if its kinetic energy is smaller than the energy threshold for the material In this case the particle is assigned a 0 kinetic energy and its energy is added as deposited energy of the parent track This check is only done if the flag ApplyCutFlag is set for the particle by default it is set to false for all particles user may change it in its G4VUserPhysicsList If the track has the flag IsGoodForTracking true this check will have no effect used mainly to track particles below threshold e The parentID and the process pointer which created this track are set e The secondary track is added to the list of secondaries If it has 0 kinetic energy it is only added if it it invokes a rest process at the beginning of the tracking e The track status is set according to what the process defined The method G4SteppingManager InvokeAtRestDoIts is called instead of the three above methods in case the track status is
91. se class will be used estimation through a Monte Carlo algorithm and the computed value will not be stored There are a few member functions to be defined for the purpose of visualisation The first method is mandatory and the next four are not Mandatory virtual void DescribeYourselfTo G4VGraphicsScene amp scene const 0 Not mandatory virtual G4VisExtent GetExtent const virtual G4Polyhedron CreatePolyhedron const virtual G4NURBS CreateNURBS EE OST virtual G4Polyhedron GetPolyhedron EE on What these methods should do and how they should be implemented is described here void DescribeYourselfTo G4VGraphicsScene amp scene const This method is required in order to identify the solid to the graphics scene It is used for the purposes of double dispatch All implementations should be similar to the one for G4Box void G4Box DescribeYourselfTo G4VGraphicsScene amp scene const 1 Scene AddSolid this The method G4VisExtent GetExtent const provides extent bounding box as a possible hint to the graphics view You must create it by finding a box that encloses your solid and returning a VisExtent that is created from this The G4VisExtent must presumably be given the minus x plus x minus y plus y minus z and plus z extents of this box For example a cylinder can say G4VisExtent G4Tubs GetExtent const Define the sides of the box into which the G4Tubs instance would fit ret
92. some special cases For example the Cherenkov process needs the energy loss information of the current step for its Dolt invocation Therefore the EnergyLoss process has to be invoked before the Cherenkov process This ordering is provided by the process manager Energy loss information necessary for the Cherenkov process is passed using G4Step or the static dE dX table is used together with the step length information in G4Step to obtain the energy loss information Any other Status of this chapter Nov 1998 created by K Amako 10 06 02 partially re written by D H Wright 14 11 02 updated and partially re written by P Arce Dec 2006 Converted from latex to Docbook by K Amako 2 5 Physics Processes 2 5 1 Design Philosophy The processes category contains the implementations of particle transportation and physical interactions All physics process conform to the basic interface GAVP rocess but different approaches have been developed for the detailed design of each sub category For the decay sub category the decays of all long lived unstable particles are handled by a single process This process gets the step length from the mean life of the particle The generation of decay products requires a knowl edge of the branching ratios and or data distributions stored in the particle class The electromagnetic sub category is divided further into the following packages standard handling basic properties for electron positron ph
93. tMassNumbar G4HadronKineticModel 4Getass vL denn SatTmeStap aetOuierRadius SatParticio Type G4VParicleScaterer bla GetNuckarFadius n eaatParticia Type SGatTmaTointeraction ChackPau Principles Pp asttuckarfadtus Hii Decanato ma PF inc ragmantsi DoLorantzBonsti AreYouHn UpdaraKingti Track SDoLar ost DoTimestept DoLor traction DoLon Contraction norransiationi GAParticleScatterer Y s etariLoopr t G4VFlekiPropagation eastNextNucleon Transport Mrrormaxicons GatExctationenergy nij v I L G4Fancy3DNucleus Figure 3 7 Level 4 implementation framework of the hadronic category of Geant4 intra nuclear transport aspect The use cases of this level are related to commonalities and detailed choices in string parton models and cascade models They are use cases of an expert user wishing to alter details of a model or a theoretical physicist wishing to study details of a particular model Requirements 1 Allow to select string decay algorithm 2 Allow to select string excitation 3 Allow the selection of concrete implementations of three dimensional models of the nucleus 4 Allow the selection of concrete implementations of final state and cross sections in intra nuclear scattering 40 Extending Toolkit Functionality Design and interfaces To fulfil the requirements on string models two abstract classes are provided the G4VParton StringMod el and the G4VString Fragme
94. ter factories in G4TrajectoryFilterFactories for example implementations 3 5 4 Other Resources The following sections contain various information for extending other class functionalities of Geant4 visualisa tion e User s Guide for Application Developers Chapter 8 Visualization e User s Guide for Toolkit Developers Object oriented Analysis and Design of Geant4 Classes Section 2 12 Status of this chapter 03 12 05 Enhanced Trajectory Drawing added by Jane Tinsley 03 12 05 Creating a new visualisation driver from Part IT by John Allison 09 01 06 Creating a new visualisation driver considerably expanded by John Allison 20 06 06 Some sections improved or added from draft vis paper John Allison Dec 2006 Conversion from latex to Docbook verson by K Amako 50 Bibliography Gamma1995 E Gamma Design Patterns Addison Wesley Professional Computing Series 1995 QGSM Kaidalov A B Ter Martirosyan Phys Lett B117 1982 247 ENDFForm Data Formats and Procedures for the Evaluated Nuclear Data File National Nuclear Data Center Brookhaven National Laboratory Upton NY USA QMD For example VUU and R JOMD model of high energy heavy ion collisions H Stocker et al Nucl Phys A538 53c 64c 1992 CHIPS P V Degtyarenko M V Kossov H P Wellisch Eur Phys J A 8 217 222 2000 VNI Klaus Geiger Comput Phys Commun 104 70 160 19977 Brookhaven BNL 63762 PYTH
95. that a track is a particle In this scheme however whenever a track object is used time is spent copying the data from the particle object into the t rack object Adopting the aggregation has a relation hierarchy requires only pointers to be copied thus providing a performance advantage 2 4 2 Class Design Figure 2 3 shows a general overview of the tracking design in Unified Modelling Language Notation CAT iim me erm CAT antis Fal In T re im els f hi 16e sacks Lim ne lector TM Tes arzorn cint F Teaze eV anmzer Sow luciana LLL eae tractor Aosercotey Ele ie betur Bide m Ll filie m kit dra Inacio da Huici fa E Zh 3 9 1 i Abla TW T ach rorem mer FieleztedAlonz3tesliskA ector 1 a CASI n pin V ror aq wipe me Fis ectadatTestliokvecto Dd Py gt M Ti fis actedScfiert iacta m eecercaey R SET sok Vecrer Apia m rrr dive E EN Miel N Cimitarra E m Did nest ne v Es N Vil delnsted cotitepMokvector N Teer Sg nv ia f bios _ m ES war in em Leite pingit iva IN y Mos 3tesargasion L J E PERA AN LT Prerbore Figure 2 3 Tracking design Design and Function of Geant4 Categories e G4TrackingManager is an interface between the event and track categories and the tracking catego ry It handles the message passing between the upper hierarchical object which is the event manager G4EventManagerz and lower hierarchical objects in the
96. tility class for navigation in volumes containing a single G4PVParameterised volume for which voxels for the replicated volumes have been constructed G4VoxelNavigation a utility class for navigation in volumes containing only G4PVPlacement daughter volumes for which voxels have been constructed G4ReplicaNavigation a utility class for navigation in volumes containing a single G4PVParameterised vol ume for which voxels for the replicated volumes have been constructed G4PhysicalVolumeStore a container for optionally storing created physical volumes It enables traversal of all physical volumes by the Ul user etc All solids should be registered with G4PhysicalVolumeStore and removed on their destruction It is intended principally for the UI browser G4VPhysicalVolume a volume positioned within and relative to a given mother volume and also represented by a given logical volume They are optionally entered into the G4PhysicalVolumeS tore G4PV Placement a physical volume corresponding to a single touchable detector element positioned within and relative to a mother volume G4PV Indexed a volume able to perform simple changes to its shape corresponds to GSPOSP and repre senting a single touchable detector element G4PVReplica a physical volume representing many identically formed touchable detector elements differ ing only in their positioning The elements positions are determined by means of a simple formula and the elements c
97. ts concrete descendants inherit from G4VGraphicsScene the method Describe Y ourselfTo can pass information of a 3D scene to a visualisation driver It is easy for a toolkit developer of Geant4 to add a new kind of visualisable component object It is done by implementing a new class inheriting from G4VModel G4VTrajectoryModel an abstract base class for trajectory drawing models A trajectory model governs how an individual trajectory is drawn Concrete models inheriting from G4VTrajectoryModel must implement two pure virtual functions virtual void Draw const G4VTrajectory amp G4int i mode 0 const 0 virtual void Print std ostream ostr const 0 See for example G4TrajectoryDrawByParticleID G4VModelFactory an abstract base class for factories creating models and associated messengers It is not necessary to generate messengers for a trajectory model that will be constructed and configured directly in compiled code If the user requires model creation and configuration features through interactive commands however there must be a mechanism to generate both models and their associated messengers This is the role of G4VModelFactory Concrete factories inheriting from G4VModelFactory are responsible for creating a concrete model and concrete messengers To help ensure a type safe messenger to model interaction on the command line the messengers should inherit from G4VModelCommand Concrete factories must implement one pur
98. urn G4VisExtent fRMax fRMax fRMax fRMax fDz fDz The method G4Polyhedron CreatePolyhedron const is required by the visualisation system in order to create a realistic rendering of your solid To create a G4Polyhedron for your solid consult G4Polyhedron While the method G4Polyhedron GetPolyhedron const is a smart access function that creates on requests a polyhedron and stores it for future access and should be customised for every solid The method 30 Extending Toolkit Functionality G4NURBS CreateNURBS const is not currently utilised so you do not have to implement it 3 1 3 Modifying the Navigator For the vast majority of use cases it is not indeed necessary and definitely not advised to extend or modify the existing classes for navigation in the geometry A possible use case for which this may apply is for the description of a new kind of physical volume to be integrated We believe that our set of choices for creating physical volumes is varied enough for nearly all needs Future extensions of the Geant4 toolkit will probably make easier exchanging or extending the G4Navigator by introducing an abstraction level simplifying the customisation At this time a simple abstraction level of the navigator is provided by allowing overloading of the relevant functionalities Extending the Navigator The main responsibilities of the Navigator are locate a point in the tree of the g
99. ws the particle to carry a list of processes to which it is sensitive A first level extension of this class defines the interface for particles that carry cuts information for example range cut versus energy cut equivalence A set of virtual intermediate classes for leptons bosons mesons baryons etc allows the implementation of concrete particle classes which define the actual particle properties and in particular implement the actual range versus energy cuts equivalence All concrete particle classes are instantiated as singletons to ensure that all physics processes refer to the same particle properties 2 9 2 Class Design The object oriented design of the particles related classes is shown in the following class diagrams The diagrams are described in the Booch notation Figure 2 13 shows a general overview of the particle classes Figure 2 14 shows classes related to the particle table Figure 2 15 shows the classes related to the particle decay table 15 G4MuonPlus Design and Function of Geant4 Categories G4MuonMinus G4PionPlus GetCutsi GetCuts s Geantind MuorPlus MuonMrus Seicus GetCutsi SelCutei M PionPius sd ce adis Secus ihe ari Senati Procal ia 1 a o G4VMeson G4VBaryon G4Vlon G4VBoson G4VLepton F v i Y Y GtLowsVecte G4LossTable lt a gt x A x iseti G4Material Ta G4ParticieWithCuts asi iron Materials SeCuss dj Rd theLesstable 0 0
100. x 1 dydx 2 y 31 vl41 y 5 The next three components are the derivatives of the velocity vector with respect to the path length So you should write the force components for dydx 3 dydx 4 and dydx 5 for your field 32 Extending Toolkit Functionality Get a G4FieldManager to use your field In order to inform the Geant4 system that you want it to use your field as the global field you must do the following steps 1 Create a Stepper of your choice yourStepper new G4ClassicalRK yourEquationOfMotion or if your field is not smooth eg Uo new G4ImplicitEuler yourEquationOfMotion 2 Create a chord finder that uses your Field and Stepper You must also give it a minimum step size below which it does not make sense to attempt to integrate yourChordFinder new G4ChordFinder yourField yourMininumStep say 0 01 mm yourStepper 3 Next create a G4FieldManager and give it that chord finder yourFieldManager new G4FieldManager yourFieldManager SetChordFinder yourChordFinder 4 Finally we tell the Geometry that this FieldManager is responsible for creating a field for the detector G4TransportationManager GetTransportationManager SetFieldManager yourFieldManager Changes for non electromagnetic fields If the field you are interested in simulating is not electromagnetic another minor modification may be required The transportation currently chooses whether to propagate a
101. yForTransients is maintained by the scene handler In fact its normal state is true and only temporarily during handling of the run duration part of the scene is it set to false see description of ProcessScene Section 3 5 1 5 If the driver supports a graphical database it is smart to distinguish transient and permanent objects In this case every Add method of the scene handler must be transient aware In some cases it is enough to open a graphi cal data base component in BeginPrimitives fillitin AddPrimitive and close it appropriately in End Primitives In others initialisation is done in BeginModeling and consolidation in EndModeling see G40penGLStoredSceneHandler If any AddSolid method is implemented then the graphical data base component should be opened in PreAddSolid protecting against double opening for example void GAXXXStoredSceneHandler BeginPrimitives const G4Transform3D amp objectTransformation G4VSceneHandler BeginPrimitives objectTransformation If thread of control has already passed through PreAddSolid avoid opening a graphical data base component again if fProcessingSolid for other solids The reason for this distinction is that at end of run the user typically wants to display trajectories on a view of the detector then at the end of the next event 3 erase the old and see new trajectories The visualisation manager messages the scene handler with ClearTransientStore just

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