NetLogo User's Guide 1. Creating a New Project: Getting Started
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1. If the agent is not specified the observer executes it The third agent in NetLogo is patches which are used to define a static environment We won t use them in this tutorial Set shape circle sets all turtle shapes to one that you ve created in the shapes editor in the Tools in the menu bar In this case we made a shape that was a simple circle then named it circle If you don t make a shape the turtles will have a default shape Finally setxy random screen size x random screen size y is really a pair of commands Each turtle will first evaluate the commands random screen edge x and random screen size y which will return each a random value between 0 and screen edge the dimension from the center to the edge of the screen along the x axis or y axis maybe 20 or so It then takes this pair of numbers and sets the turtles at these random coordinates Press your setup button when you ve written the code You can see the turtles quickly spread out in a rough cluster Notice the density distribution of the turtles on the Graphics Screen Press setup a couple more times and watch how the turtles arrangement changes Can you think of other ways to randomly distribute the turtles over the screen There are lots of ways Note that if a turtle moves off the screen it wraps that is comes in the other side When you re satisfied that the button does what you want it s time to write your next procedure But first you should2. If you go back to your interface window and click on vas y un pas you will see that yellow turtles become gray on the next step 3 Adding local vision and synchronization Our fireflies move now around in a rather natural manner and flash every 10 steps Why are they not synchronizing Well simply because we still haven t implemented the mechanism that is supposed to lead to synchronisation when a neighbouring firefly flashes then the compteur is set back to seuil We therefore need a routine regarde that detects flashing fireflies in the neighbourhood to regarde if count turtles in radius 1 with color yellow gt 1 set compteur niveau end Do you understand what the test does It first counts the flashing fireflies in a Moore neighbourhood and then checks if this number is larger than one This routine is called after augmente compteur if the firefly is not flashing itself and is again sensitive for other flashes to vas y bouge ask turtles augmente compteur if compteur gt fenetre and compteur gt seuil regarde ifelse compteur lt seuil set color yellow set color gray end 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 7 of 9 Thats it the mechanism that should synchronize flashing is now implemented Does it work 4 Adding observer windows and visualization of the synchronizing process We now have a functioning model o
3. command First each turtle picks a random integer between 0 and 359 random doesn t include the number you give it Then it sets its heading to be this number Heading is measured in degrees clockwise around the circle starting with 0 degrees at twelve o clock fd 1 After each turtle does that it moves forward one step in this new direction Why couldn t we have just written that in vas y We could but during the course of building your project it s likely that you ll add many other parts We d like to keep vas y as simple as possible so that it is easy to understand It could include many other things you want to have happen as the model runs such as calculating something or plotting the results Each of these sub procedures could have its own name Each time you click now on vas y NetLogo will execute the commands in bouge But it would be nice if NetLogo would repeat bouge indefinitely until you click again on the button This can be done easily create another button with the Name vas y and the code vas y but this time check the forever box in the editing dialog box The vas y button is a forever button meaning that it will continually execute its code until you shut it off by clicking on it again After you have pressed setup once to create the burls press the vas y button Watch what happens Turn it off and you ll see that all turtles stop in their tracks You could probably jump off from here and start experimen
4. program what to do with such strange characters that is displayed in its own monitor and a routine that counts the number of flashing fireflies globals ticks allume to compte allume set allume count turtles with color yellow end compte allume can be called at the end of the vas y routine and the monitor for allume is created as the one for Ticks Simulating now step by step permits to determine exactly at which step more than 80 of the fireflies are flashing synchronously Try to do it Got it Takes too much time I agree completely It would be nice to have a graph that plots the number of allume as a function of Ticks Again NetLogo provides the tools to do this We first need routines that initialize and update this graph during run time In the setup procedure add a call to the routine creer graph to creer graph set current plot Lucioles allumees auto plot on set plot x range 0 100 set plot y range 0 nombre set plot pen lucioles this line is obsolete in 1 3 set plot pen color red end and in the vas y routine add a call to faire graph to faire graph set current plot Lucioles allumees plot allume end 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 8 of 9 What we re plotting is the number of flashing fireflies at some given time Step by step the commands in our creer graph procedure do the following e Select the first plot window e
5. save your work in order to preserve it in case of a computer crash create a folder with your name on the harddisk C and then use the menu File gt Save As to save your project in this folder During this tutorial it will be a good idea to save your work from time to time with the menu File gt Save Now to the next procedure make first a button called vas y un pas Again begin by creating a button with the Display Name vas y un pas and the code command vas y dures a f Component Type Button Delete Edit 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 4 of 9 Display Name vas y un p Code sees KI But what is bouge Is it a primitive like fd is No it s a procedure that you re about to write right after the vas y procedure Then write the procedure to vas y bouge end to bouge ask turtles set heading random 360 fd 1 end Did you notice anything unusual like a change to smaller characters Bad luck you have a french keyboard and to type you have to press alt which is interpreted by NetLogo as a shortcut to reduce letter size You can revert the change with the menu zoom Normal Size or ctr1 and avoid this bug in the future by copying and pasting Now look at the procedure line by line ask turtles says that each turtle should execute the commands in the brackets set heading random 360 is another two step
6. this effect biologically Any other intuitions Write a nice little report that summarizes your results and interpretations 1 3 pages It may be in French ps for more information on NetLogo and the detailed definitions of NetLogo commands you can view the documentation provided with your installation of NetLogo Start your web browser Netscape Explorer and open the local file docs index htm1 in your Netlogo Folder with the menu File gt Open File or suchlike You can also visit directly the NetLogo internet site http ccl northwestern edu netlogo it has lot s of useful information 16 octobre 2003 Christian Jost 9 of 9 10 20 03 11 41 AM
7. NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 1 of 9 NetLogo User s Guide Programming Tutorial for synchronizing fireflies adapted from the official tutorial NetLogo is a freeware program written in Java it runs on all major platforms You can download a version for your computer from http ccl northwestern edu netlogo This tutorial was developped with Netlogo version 1 0 but the commands are equally valid for version 1 3 a single difference is indicated in the text e 1 Creating a New Project e 2 Developing Your Model e 3 Adding local vision and synchronization e 4 Adding observer windows and visualization of the synchronizing process e 5 Homework the bad news This tutorial describes a complete project built up stage by stage with every step explained along the way 1 Creating a New Project Getting Started To create a new project select New from the the File Menu Let us first explore the Command Center which has a command line as in Scilab the other freeware program we will use in this module We first create 100 turtles by the command O gt crt 100 NetLogo creates with this command 100 turtles why turtles well that s the name the creators of NetLogo gave to their virtual individuals and we will adopt their terminology for the moment But where are they In fact you will only see one on the screen because one turtle sits on the other To show them all
8. Turn on automatic rescaling of the plot window axes useful if you re plotting some value over time as we are e Set the range of the x axis both minimum 0 and maximum 100 e Set the range of the y axis again both minimum and maximum because we ll have at most nombre fireflies at peaks our maximum is the number of fireflies Name the first plot pen to be the current active plot pen in this graph e Set the plot pen color to be red Then in faire graph we select the plot Lucioles allumes and the plot pen lucioles currently redundant since there s just one but maybe we ll add more later and then we plot a point The plot command draws a connected graph at the current x coordinate and y coordinate and then updates the x coordinate by automatically But where will it draw Go back to the Interface window there you can add a plot widget to your model edit it and change its name to In order for set current plot Lucioles allumees Lucioles allumees the exact same name used in the code Now reset the project and run it again Watch the graph in the Plot Window You might try running the model several times under different settings i e different values of nombre and watch how fast the graph reaches 80 18 9 909 j aJ tta a AkKjo0aj B Compile ret E pha Slider Switch Montter Tact Piot Campile o Prt TH Tl 83 gt wrap wey g van y eens 1 Lecietes Allames Pern 5000 So now you ha
9. ariables in setup to reasonable values e g fireflies should be yellow when flashing and gray otherwise to setup ca crt nombre ask turtles setxy random screen size x random screen size y set shape circle set compteur random round 10 10 est la duree d un cycle set seuil 1 set niveau seuil set fenetre 1 pas de periode insensible ifelse compteur lt seuil set color yellow set color gray end We used here a new NetLogo command ifelse test commands commandsz2 that executes commands 1 if test is T true commands2 otherwise Note also that it is quite unnatural for 5 of 9 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 6 of 9 fireflies to turn around completely randomly in the bouge routine they rather do a random left wiggle and a random right wiggle before continuing their path The new bouge routine thus becomes to bouge ask turtles set heading heading random 90 random 90 fd 1 end In vas y we have to add a routine that increases compteur at each step and resets the firefly color according to the value of compteur to vas y bouge ask turtles augmente compteur ifelse compteur lt seuil set color yellow set color gray end to augmente compteur set compteur compteur 1 if compteur 10 set compteur 0 end We use here the new command if test commands that is a simplified version of ifelse
10. f synchronizing fireflies It can be used to study the influence of the different environmetal variables on the synchronization process How long does it take to synchronize 80 of the fireflies How does the number of fireflies influence this time How does the value of fenetre influence this time This playing around with the model helps to detect new patterns and to formulate new hypotheses that can then be tested under natural conditions To do so we first need to add a global variable ticks that keeps track of the number of steps our simulation has run Add the line globals ticks after the turtles own command Add a command in the setup routine to set it to 0 you should now know how to do this and increase it by 1 in the vas y routine Then we should display this number on the screen Have you already seen the button we need to do that Exactly we will monitor the ticks so simply click on the Monitor button and create it in the Graphics window telling it to display the value of ticks Now you should see 0 in this monitor after setup and it should increase by one each time you click on vas y un pas Similarly it would be nice to know how many fireflies are flashing at each time step For this we need a second global variable allume this should be allum but using accents in english software is always playing with the devil most english programmers don t even know accents exist and thus have often simply forgotten to tell the
11. g Your Model From Turtles to Fireflies with their variables So now we ve got 100 turtles aimlessly moving around completely unaware of anything else around them Actually we want our turtles to be fireflies and to behave like them that is to synchronize their flashing when they meet other flashing fireflies For this we have to give our fireflies some variables compteur which is the internal clock of the firefly it will flash when its value is 0 and increase at each step to a maximum of 9 after which it is set back to 0 seuil which is the value of the compteur at which the firefly stops flashing niveau which is the level the compteur is set to when seeing a flashing firefly and fenetre which is an insensitivity period after flashing during which the firefly doesn t see any other fireflies Well let s do all this step by step First add the variables at the top of the procedures window turtles own compteur horloge de chaque luciole va de 0 a 9 auquel valeur elle clignote seuil seuil du compteur auquel la luciole arrete le clignotement niveau niveau auquel une luciole met son compteur quand elle voit un voisin clignoter fenetre une luciole ne peut changer son compteur s il est lt fenetre The semicolon indicates that the rest of the line contains comments that are ignored by NetLogo and help a reader to understand the code but you do not have to include these comments in your current code We now have to set this v
12. se button and select the Edit menu type Initialisation in the Display Name Window and click ok Component Type Button setup _ at iT J Forever Observer At this point Errors will turn red That s because there is no procedure called setup Errors Compile All Halt Error h 3 oj 2 Compile Halt Find Find Again ask turtles setxy random screen size x random screen size v set shape circle 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 3 of 9 One line at a time ca is short for clear all another acceptable NetLogo primitive that does the same thing This command will blank out the screen initialize any variables you might have to 0 and kill all turtles basically it wipes the screen clean for a new run of the project crt 100 will then create 100 turtles Each of these turtles will begin at the origin at location 0 0 That s why you only see what looks like one turtle they re all on top of each other lots of turtles can share the same patch Each of these newly created turtles has its own color evenly distributed through the range of NetLogo colors and its own heading evenly distributed around the circle ask turtles tells each turtle to execute independently the instructions inside the brackets This is equivalent to selecting the command line T gt Note that ert is not in brackets
13. ting with other turtle commands That 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 isn t such a bad idea Type commands into the Command Window like set color red or add them to setup vas y or vas y un pas Note that when you enter commands in the Command Center you must choose T gt P gt or O gt in the drag down menu on the left depending on which agents are going to execute the commands T gt commands is identical to O gt ask turtles commands and P gt commands is identical to O gt ask patches commands patches are a way to incorporate a dynamic environment e g grains transported by ants but we won t use them in this tutorial You might try typing T gt It random 45 for left turn instead of T gt set heading random 360 or any other NetLogo command that applies to turtles or patches But first we will make the number of turtles a user defined variable Instead of saying crt 100 in setup say crt nombre where nombre is a slider variable and create a slider from the graphics toolbar just as you created the buttons with minimum value 0 and maximum value 2000 in steps of 10 When you change now the number of turtles with the slider and click Setup again NetLogo will display the new number of Turtles Play around It s easy and the results are immediate and visible one of NetLogo s many strengths Regardless the tutorial project continues 2 Developin
14. ve a nice framework for exploring the fireflies synchronization problem using all sorts of NetLogo modeling features buttons sliders monitors and the graphics and plot window displays You ve even written a quick and dirty procedure to give the turtles something to do And that s where this tutorial leaves off You can continue it if you d like experimenting with different variables and algorithms to see what works the best what makes the most turtles reach the peaks Alternatively you can look at other models or go ahead and build your own You don t even have to model anything It can be pleasant just to watch patches and turtles forming patterns or whatever Hopefully you will have learned a few things both in terms of syntax and general methodology for model building 5 Homework the bad news As a homework use your program to explore how the number of fireflies influences the time it takes to synchronize at least 80 of the fireflies set nombre to 10 20 50 100 200 500 1000 and get a confidence interval of this duration by repeating each simulation a couple of times With a fixed number of fireflies e g 500 guess intuitively how the value of fenetre influences this time 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 Modify your program to explore whether your intuition gave you the correct answer use the values 0 1 2 and 3 for fenetre How do you interpret
15. we have to make them move away from the center Since this only concerns the turtles we have to click on the o gt in the command center and change it to T gt like Turtle then type the command T gt fd 10 Command Center 10 20 03 11 41 AM NetLogo User s Guide file Users jost Documents enseignement lectures Cours TD 2 2 of 9 They now moved forward 10 steps You can move them further away a random number of steps between 0 and 9 with T gt fd random 10 Finally with the command ca clear all in the observer line O gt you will make disappear all the turtles Typing all these commands on the command line permits to explore the functioning of NetLogo commands but this is not very efficient if we want to repeat this sequence of commands several times NetLogo permits to write commands also in a procedure Start doing this by creating a once button called setup This button will do just that initialize your project You create this button by clicking on the Button icon on the Graphics Toolbar and then clicking where you want the button to be in the Graphics Window When the button appears click on edit on the Toolbar and type setup in the code box When clicking ok a button will be created that is called setup and will execute the procedure setup when pressed In fact you could name it something else for example Initialisation Try it out move the cursor on the button click the right mou
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