user`s manual
Contents
1. Osi OCG fFm A Pe A amp If you have the Basic version of the software the header will say STELLA 6 0 rather than STELLA Research 6 0 Overview of the environment You are looking at one of the three levels in the STELLA software This is the Map Model level Here you will perform your rendering and numerating of mental models You may also simulate and do some communicating from within this view The two other levels are accessed by clicking the up and down arrows located near the top of the left vertical window frame Don t click them yet The up arrow will take you to the Interface or communication level The tools available there will enable you to construct an interface for your models allowing you to quickly turn them into discovery oriented experiential vehicles for people who may not have been involved in the rendering process We ll visit this level later in the tutorial and construct a Flight Simulator interface for your population model This will enable your colleagues students teachers etc to share in the understanding that emerges as you create the model The down arrow takes you to the basement It s dark down there It s where the equations live If you like equations you ll love the basement If you don t no sweat You never have to go down there because any equations you may need can be created from within dialogs that appear in the Map Model level We will MM H2. births The arrowhead on the flow pipe illustrates the direction of flow in this case it points into the stock because births is an inflow to Deer Population The circle with spigot in the center of the flow pipe is called a flow regulator The circle ultimately will contain the logic or decision rule that adjusts the volume of the flow e directs the spigot to open wide or shut itself down Note that the flow in this case emanates out of a cloud Sometimes as you ll see flows empty into clouds Clouds denote a boundary point of the model The cloud out of which the births flow is emanating means we are not going to include within the boundary of the model the source of the flow the stock that is being drained by the flow of births into the Deer Population stock Let s pause briefly to savor the important distinction between a stock and a flow the nouns and verbs of the STELLA software language Stocks represent conditions how things are Flows represent actions how things are going When all actions cease all flows go to zero But notice that the conditions 1 e the magnitude of the stocks would remain wherever they were at the instant the freeze took effect So for example if you stop putting food in your mouth that s right freeze that chip in mid air your stomach will reflect the cumulative amount of chips you have deposited before the freeze occurs
3. s in the equation listing They appear because we will need to provide some numerical information before a computer simulation can be conducted We ll get to that soon For now click the up arrow located in the upper part of the left frame of the window to exit the basement and return to the Map Model level Now click the Globe icon located near the top of the left frame of the Map Model window Note that the icon changes to an X You screen should now look like this MM High Performance Systems Inc All rights reserved 11 2 yourname stm Os 0t ORO Pm A MEFS ESLG Deer Population bith traction death traction By the way we recommend that you save your work every now and again Choose Save from the File menu and type the name of your model The program automatically attaches the necessary stm ending for Windows users The globe indicates that you are in mapping mode The X indicates that you are in numerating or equations mode Note the s that now appear on each building block in your map They indicate the need for numerical or equation information Your model will not be in computer simulatable condition until all s are extinguished by providing the required information Let s see how this process works Double click on the Deer Population stock The following dialog box should appear MM High Performance Systems Inc All rights re
4. OK resume snacking MM High Performance Systems Inc All rights reserved 8 Recognizing the distinction between stocks and flows is absolutely critical to accurately capturing the dynamic behaviors a system will generate We don t have time to provide a full explanation here but to get a quick glimpse of the differences consider the basic structure you just created Can you see how it could be possible for the flow of births to be increasing but the Deer Population to actually be decreasing at the same time Hint consider the other side of the spectrum the natural population control outflow known as death We ll be adding this flow to the map soon Without making the distinction between stocks and flows we would not be able to understand how the volume of a flow could move in one direction while the magnitude of a stock moves in the opposite direction By the way you may notice that in our rendering of this map we have used first letter caps when naming stocks and all lower case for naming flows This helps to make the difference between these two types of variables more distinct particularly when they occur in lists within dialogs where we might not be able to see the different icons associated with each Distinction noted we are now ready to employ the two remaining building blocks the connector and converter to complete the logic of the deer population growth piece of the model It makes sense that the number of bi
5. Uniflows allow flow only in the direction in which they point Births clearly only flow into Deer Population so uniflow is the choice and the default The Required Inputs list contains two variables Deer population and birth fraction These variables are in the list because we drew connectors from them to the births flow regulator The dialog box is now telling us that we are required to use both variables in defining the births equation Suppose we didn t use the Required Inputs Try it Type or click in a number then click OK You should receive the alert Unused input Deer_Population You can exit the dialog without including both required inputs in the equation but the on the surface of the building block will not extinguish until you include all the required inputs in the equation The software enforces a one to one correspondence between what you see on the diagram and what appears in the underlying equation Click once on Deer Population to enter it into the equation Now suppose we decided we also wanted to include a second group of deer the Extra Deer Population Type or click the then type extra_deer_population and add it to the equation Click OK MM High Performance Systems Inc All rights reserved 14 You should receive the message Not the name of any object on the Diagram The software not only ensures that what you see is what you get it also ensures that if you don t see it y
6. Table E218 PM Tue Feb 01 2000 Table 1 Untitled Table Deer Population Once again your results may not be exactly the same We did make some minor changes in the Table dialog First within the Table dialog box we unchecked the Vertical orientation option which makes our results run you guessed it horizontally We also unchecked the Every DT option below the words Report Interval Instead we told the table to report every 1 time period We also formatted Time and Deer Population to get rid of the two decimal points After all we don t usually see 33 of a deer in the woods To format Deer Population we must first exit the Table dialog window by clicking OK Then we double clicked on Deer MM High Performance Systems Inc All rights reserved 17 Population in the Table and chose a precision of 0 We did the same for Time Run again and your results should be identical to those shown on the previous page Step 3 Analyzing So now that we ve simulated what can we learn from our model What we ve observed so far does not conform to the overshoot and collapse phenomenon that we saw at the beginning of the exercise Instead we see smooth exponential growth Why don t we see overshoot and collapse Is it possible for this very simple structure to generate growth and subsequent decline in population Fortunately the software provides powerful tools for answering these sorts of questi
7. boxes shown above Click the Set button which now says De set to Implement the scale To define a Table Pad page follow the same procedure for entering variables fram the Allowable to the Selected list Other options within the Table Pad dialog are fairly sel explanatory Refer to the Online Help files for more detail MM High Performance Systems Inc All rights reserved 42 Communicating Illustration 8 Using the Text Tool i STELLA Research 6 0 Bal Step 1 Click to select the text tool AT Step 2 Click to deposit a text block twill look like this A cursor willbe flashing in here Just begin ping Step 3 To access the text block s dialog move the cursar tothe border ofthe block When it changes from an l beam to an arrow double click to open up the dialog Step 4 Choices within the dialog are straightforward MM High Performance Systems Inc All rights reserved 43
8. flow length Usually you will either be dragging the flow into or out of a stock though creating flows without attached stocks is possible Both are illustrated below Creating an inflow A Stock O Oo S T EEH Position the cursor Click and hold then drag When the arrowhead hits the to the left ofthe stock wall the stock will highlight to indicate that a connection has been made release your click Creating an outflow A Stock _ Nania Click and hold then drag out through the right wall Fosition the cursor inside the stock When the pipe extends to the desired distance release your click lick and hold on the stock then drag it Step 3 ifthe flow doesnt stick to the stock until the index finger of the Hang cursor is on as illustrated below top ofthe cloud causing it to highlight Release your click A stock e O q noname noname 2 MM High Performance Systems Inc All rights reserved 37 Illustration 3 Re positioning Bending and Reversing Flows A Stock A Stock a flow Flow connects to stock Click and hold an fow too low on wall regulator then slide fow Click and hald cloud up the wall then slide it down Pipe bends down To re position flow from side to bottom click and hold cloud then re position the cloud as shown flow will automatically re position itself as shown To bend a flow drag to the point where you wi
9. resizing handles appear to make the title clearer And now you re ready to share your model with the MM High Performance Systems Inc All rights reserved 33 world Actually not quite Presentation is very important and it s a good idea to keep input and output devices well separated for clarity Take a look at how our final control panel turned out Deer Dynamics Control Panel OC tain a a 1 Deer Population 1 S00 death traction D 1900 00 1902 50 1905 00 1907 50 1910 00 Graph 1 Untitled Years 10 00 Phi Tue Feb 01 2000 Hack to Main Menu Final Considerations This Flight Simulator is a decent start but in its current form it is not truly a learning environment We have not introduced policy choices that the user can make to try to prevent the overshoot and collapse All we have done is create some easy ways to change assumptions that are already built into the model To facilitate learning the Control Panel should include an ability to reintroduce deer into the system from external sources or raise a bounty on predators remember predators aren t even built into this model In the interest of time we haven t added these options However by this point you should feel comfortable enough to explore adding these features yourself with help from the Electronic Help files that you can find within the software MM High Performance Systems Inc All rights reserved 34 This conclude
10. 4 Untitled Double click In here to open dialog Click lock ta keep graph page frozen e not overwritten 3 00 9 00 127 00 wig BF Graph 1 Untitled 12 01 AM Wed Feb 02 2000 7 Click dagear when there are multiple pages on pad in order to page up or down MM High Performance Systems Inc All rights reserved 4 Illustration 7 Defining a Graph or Table Pad Page Choose a Graph Type _ TIME SERIES is variables eA a over time SCATTER is A S Y BAR is a kbar graph Graph Type f Time Series C Scatter C Bar C Sketchable arab l Comparative Comec ats M Benchmart you to enter a sketch of Allowable Selected how you think x will C Deer Population il SEDANE NEEN L Vegetation A To ent abl o enter variables paul eal a into the Selected ao consuming 4 list so they can be a deaths en plotted double click them in the I Show Numbers On Plots Tithe Untitled Allowable list W Show Grid Thick Lines T Make 5 Grid Segments SKETCHABLE enables To add a new Min Ma j _ _ _____ _ l page tothe Pad E De Set Page 1 e click the ea ze up arrow Display li h 3 Cancel To set a scale for a variable click on the variable for variables if you wish the set to share a common scale in the Selected list Then click the double headed arrow that will appear to the right of the variable You will then be able to enter a Min and Max value for the scale In the
11. 8 stocks can radiate information or send signals that reflect their magnitude MM High Performance Systems Inc All rights reserved 39 Illustration 5 Defining a Graphical Function step 1 In the Converter dialog box click to enter the input variable expression step 2 Click the B Graph button Step 4 Click and hold and drag through the a i E epee grid to produce a curve or click on each vertical line and the curve will ump to where you click Alternately you can type values into the Qutput column and the curve will be created that way Range box w 2 000 an i oe ne step 3 Determine a range for the input and output variables Enter it into the range boxes SW amp m Range box i n Ee ee Ei ry _ iiss Data Points Converts N 0 000 2 000 continuous B i Edit Output sumer E shock target stock of discrete line Fange box Range box segments To Equation Delete Graph Cancel MM High Performance Systems Inc All rights reserved 40 Simulating Illustration 6 Creating a Graph or Table Pad Heo OEO M A Me y 2 F A se Step 1 Click to select Graph tool Table tool is here as gt Step 2 Position graph cursor where Table Pad YOu wish to deposit a graph pad Operation Step 3 Click to deposit a graph pad pimi IS exactly page 1 ofthe pad will appear EEE analogous ta l l raph Fad Click pushpin to stick pad to surface
12. Getting Started with STELLA v 6 0 HPS MM High Performance Systems Inc The Systems Thinking Company http www hps inc com Table of Contents Welcome The Basics A Tutorial for New Users Appendix Basic Software Operations amp Features Rendering Illustration 1 Depositing Naming amp Re positioning Stocks Converters and Nameplates Illustration 2 Hooking up Flows Illustration 3 Re positioning Bending and Reversing Flows Illustration 4 Hooking up and Re positioning Connectors Illustration 5 Defining a Graphical Function Simulating Illustration 6 Creating a Graph or Table Pad Illustration 7 Defining a Graph or Table Pad Page Communicating Illustration 8 Using the Text Tool MM High Performance Systems Inc All rights reserved 36 36 37 38 39 40 41 42 43 Welcome Welcome to the STELLA software Getting Started Tutorial This tutorial provides an experiential introduction to the basic operations and features of the STELLA software for new users The STELLA Electronic Help Files that accompany the software comprehensively describe software operation and features in much greater detail The approach here is selective not all features are illustrated and context rich Through a case study involving deer population you ll progress through an organized series of diagrams that illustrate how to perform the basic operations and use the basic features of the soft
13. and side of equation here Focus on the first equation the one for Deer Population It says What you have now is what you had an instant ago plus whatever flowed in over the instant minus whatever flowed out over the instant Or The magnitude of Deer Population at time t the current time is equal to the magnitude of Deer Population at t dt one time unit or dt delta time in the past plus the number of births that flowed in over the instant minus the number of deaths that flowed out over the instant Flows which are defined as occurring over a unit of time over a year for example are multiplied by the length of the instant dt which is usually less than a full time unit so that only the instant s worth of the flow is added to or subtracted from the stock The software automatically sets up this generic bathtub accounting equation every time you create a stock The generic equation simply totes up the flows into and out of a given stock during each time period over the course of a simulation The equation reports out the resulting current magnitude of the stock at each point in time You don t have to worry about writing this accounting equation because the software does it for you It figures out whether to add or subtract associated flow values based on the direction in which the arrowheads on the pipes point i e do they point into or out of the stock Note all of the
14. ate a very basic control panel containing only a few items First drop a Graph Pad onto the screen Double click on the graph and enter Deer Population into the Selected List Scale it from 0 to 500 remember you must click once on Deer Population to highlight it then click on the double headed arrow to make the scaling boxes active Click Set Scale then Click OK You may notice that the graph is displaying 12 units of generic Time on the x axis If you think back to the very beginning of this exercise you ll remember that we were discussing the overshoot and collapse trend that occurred over a number of years So let s change the time units of our model so it will be reflected on the graphs and tables Choose Time Specs under the Run Menu You will get this dialog MM High Performance Systems Inc All rights reserved 30 2 a Change the length of simulation so it runs from 1900 to 1910 Select Years as the Unit of time Run the simulation again and yov ll see that your graph is now displaying the proper time units Now let s create an interface that will let others play with the model you have built First make sure you have centered your graph and pinned it down Then choose the Slider Input Device from the Tool bar It s the 10 icon from the left Click once to deposit it Then double click anywhere on it to open its dialog which will look like this eee births om consumi
15. dialog Look on the lower right of the dialog to find the word Button the default name for the button Replace the text by typing Go To Main Menu and Click OK Click OK again and look at your button it should have the words Go To Main Menu on it You may wish to use the paintbrush to change the color and you can resize the button by clicking once on the border to select it Resizing handles will appear Click and hold any handle and drag to resize the button Scroll down to a blank space You may need some more paper To get it deposit a button in the blue space Then deposit one more button and name the two buttons Explore the System and Fly the System Then scroll back up to your Welcome screen and double click on the border of the Go To Main Menu button The dialog will appear again Select Navigate under Button Purpose Then click the Define Navigation button Click and hold on the drop down menu it says None that enables you to select a screen transition effect Select Iris In Select Effect to Black Then click the Navigate To button located next to the camera icon Your cursor will become a camera DO NOT click on any page surface just yet Scroll to the screen you created that contains the two new buttons on it Scroll until the buttons are centered on the screen then click once on the screen The camera will take a picture of that screen and remember it as t
16. e options for sharing your insights with others This is one of the most important and powerful aspects of the STELLA software You could simply let others look at your model and marvel Or you could use STELLA to create an interactive experience that will let them discover and experience the insights that you have uncovered We will now create a sample interface that will enable us and others to fly the model to see how we can impact the growth and decline of the Deer Population If you do not wish to take the time brief though it may be to create an interface you have two options You can stop now and come back later just click Save in the File menu or you can open the deerA model and fly using our interface MM High Performance Systems Inc All rights reserved 25 If you ve decided to continue click the up arrow at the top of the left frame of the Map Model window Here s what you ll see and what some of the icons are called hover over the tools to see their names 4 yourname stm 39 BPORMnOBs measa AM mg SY Slider Input Text Bos Buttor Device Warming Graphical Device Graphics Input Device Frame Numere Display The Interface or communication level is used to create interfaces for your models We ll put together a very simple one here to illustrate some of the interface features and then give you a chance to fly this ecosystem Let s begin by creating a welcome
17. e you should expect to iterate like this through the rendering and simulating steps multiple times As we said before render a little chunk simulate Render another little chunk simulate This will keep you in control of the process Round 2 Mapping Numerating and Simulating In order to get Deer Population to rise and then fall death fraction needs to become variable rather than remaining a constant Suppose our model allowed the death fraction to increase as the Deer Population increased This could reflect the notion that as the Deer Population rises the strain on a fixed food supply increases The STELLA software provides a way to represent such a relationship It s called a graphical function Let s incorporate a Deer Population death fraction relationship into our model MM High Performance Systems Inc All rights reserved 19 Draw a connector from Deer Population to death fraction as shown below Deer Population ER ee death traction Double click on death fraction Click once on Deer Population in the Required Inputs list and then click once on Become Graph A blank grid will appear Following the instructions in Illustration 5 make death fraction look like this you will likely have to click on the various numbers in the output column and type in these numbers to get the exact values Data Points Ii Deer Population Edit Output To Equation Delete Graph Cancel Notice first tha
18. egetation declines death fraction will increase Double click on the consuming flow Notice that the Required Inputs are Deer Population and vegetation per deer If we know the magnitude of Deer Population and how much each deer on average consumes we can easily calculate the total consuming Define the consuming flow to be Deer_Popluation vegetation_per_deer Click OK Then define vegetation_per_deer as a constant 15 and click OK The second link is between Vegetation and death fraction Double click on death fraction and select Vegetation from the Required Inputs list Click once on the To Graph button and set up the scales on the axes and the curve as follows MM High Performance Systems Inc All rights reserved 23 Jupu 1 000 a er oo A Tr Data Points j A Venalaton Edit Output To Equation Delete Graph Cancel Before clicking OK let s examine the relationship to see if it makes sense The graph says that as Vegetation increases the death fraction will decrease Or as Vegetation decreases the death fraction will rise Click OK to exit the dialog Define the remaining undefined objects as follows Vegetation initial 3500 Regenerating Vegetation regeneration_per_plant the more vegetation the more reproduction Regeneration per plant 5 one new plant is produced for each two plants per year Now we re ready to run the model Open your Graph Pad and examine the behavior of Deer Po
19. g the dynamics of population growth and decline In this tutorial we will examine the dynamics of a deer population in a very simple forest ecosystem The deer population is regulated by food supply and predator population In 1900 in response to pressures from ranchers and farmers a 50 bounty was placed on predators because of attacks on livestock In the next 40 years an overshoot and collapse pattern of growth and decline emerged in the deer population The deer population grew until it far exceeded what its food supply could support Then starvation on a massive scale occurred This pattern can often occur in the natural world The following graph illustrates the behavior of the population MM High Performance Systems Inc All rights reserved 4 Deer Population 200000 100000 Your mission should you choose to accept it is to use the STELLA software to answer the following questions What are the relationships that generate overshoot and collapse and what are the leverage points for reestablishing a balance We ll take you through a step by step progression that will help you discover the answers Step 1 Rendering a Mental Model Mapping This step consists of two sub steps mapping and numerating transforming the map into a computer simulatable model Launch the STELLA software Your screen should look like this MM High Performance Systems Inc All rights reserved 4 STELLA Research 6 0
20. he illustration and decide what font size you want small medium or large OK your way out of the button and click on it A yellow pop up text box will appear You can move the box by clicking on the blue header and dragging You can resize the box by clicking on its border and dragging And you can close the box by clicking on the close box x in the upper right corner The Explore the Model button will illustrate a unique 6 0 feature called Storytelling Selecting this option which is available in the button dialog you can customize the unfurling of the structure of your model one piece at a time providing commentary along the way in the form of text movies sounds or graphics Let s see how Double click to the button border and choose Storytelling Click the Create Story button and you will see a dialog that looks like this Allowable Story Sequence LC Deer Population C Vegetation coe births oot consuming oo deaths oot regenerating a birth fraction CI regeneration per plart a vegetation per deer z death fraction Annotate with D Hothine Eiei f Sound Biait leet E mapie B Hove Cancel Double click on several variables to enter them into the Selected List in the order in which yov d like them to be unfurled Then click once on the first item in the Selected List to highlight it The 5 radio buttons associated with Annotate with will become activated You can assig
21. he maA MEF SA The four Building Blocks In the STELLA language The first of these building blocks the rectangle is called a Stock Stocks are used to represent things that accumulate Water in a stream or reservoir accumulates So does mass fear knowledge or population It is the last of these accumulations that will impact the initial rendering of our deer population model Let s render a stock of Deer Population since we will be tracking and trying to influence the behavior of the deer population in our model To do so follow the directions in Illustration 1 which appear in the Appendix that follows this tutorial When you ve successfully completed this operation your STELLA software page should look like what you see here MM High Performance Systems Inc All rights reserved 7 2 STELLA Research 6 0 Heo ORO m A MEFS a Deer Population Next we will add a flow into the stock of deer population Since we know that deer population rises and falls but we ll deal with that later we must have a way for it to increase We ll represent an increase in population by creating a flow called births As deer are born they become members of the deer population Hook up this flow into the Deer Population stock follow the directions in Illustration 2 in the Rendering section of the Appendix When you complete this operation your diagram should look like this Deer Population
22. he place to which to navigate OK your way out of the dialogs and try out your Go to Main Menu button Once you ve navigated to the screen with the two buttons you may want to take a bit of time to reposition the buttons add some text and deposit another button titled Back to Welcome Follow the same steps using camera navigation to navigate back to the Main Menu Choose Effect to Black and select Iris Out as an effect OK out of the dialogs and test your button Now you can easily navigate between pages The following is our Menu Screen MM High Performance Systems Inc All rights reserved 27 MAIN MENU Explore the System Fly the System Hack to welcome Define the Explore the System button as a navigation button Make it navigate to a new screen on which you should place a text block with the text Explore the System in it Navigate to this screen and deposit two buttons Label the first Instructions We will set this button up as a Show Info button as shown in the illustration Label the second Explore the Model EXPLORE THE SYSTEM Click on the button below to explore the structure of this model This button can contain either small medium or large size text Explore the Model MM High Performance Systems Inc All rights reserved 28 Double click to open the Instructions button Select the Info option and click Show Info Then type in the text in t
23. igh Performance Systems Inc All rights reserved 6 travel to the basement later in the tutorial For now hang with us on the Map Model level Producing a first map It s almost always a good idea to render a mental model or a collective mental model if you re doing this in a group in little chunks one chunk at a time rather than seeking to map the whole thing at once You spit out a little chunk thinking about what you see as you go You then numerate simulate and ruminate on the results Next you spit out another little chunk and repeat Following this iterative bite sized approach will keep you in control of the process It s very easy for the process to spin out of control because the software makes rendering so easy In this part of the process the software is acting as a word processor for the mind Anyone can generate a lot of words with a word processor Writing a coherent essay short story or novel is quite another thing altogether The same is true with the STELLA software Think quality not quantity Go slow not fast Write clear simple mental models All of your writing rendering will be done with only four iconic building blocks One of the beauties of the STELLA Software is its very sparse yet very powerful language set The building block icons are the first four icons on the left of the horizontal palette that adorns the top border of the software 2S STELLA Research 6 0 C
24. k the running man in the lower right corner and use the forward arrow to run You ll have to double click on the graph pad icon to make the graph reappear The graph page should look like this MM High Performance Systems Inc All rights reserved 15 2 Untitled Ss 1 Deer Population 1 1500 Uae aay EESE E E A eset T E E E E E E E E aaa E E se ecenas E ie 0 00 3 00 6 00 9 00 12 00 Neg BF Graph 1 Untitled Time 12 29 PM Tue Feb 01 2000 2 Actually your graph won t look exactly like this The numerical scale for Deer Population has been reformatted to remove the two decimal points from the scale If you wish to reformat the variable make sure you have exited the graph dialog then double click on Deer Population on top of the graph page to pop up the formatting dialog box and choose 0 Also make sure that you have scaled the Y axis to begin at 0 and end at 1500 See Illustration 7 in the Appendix for help You may also use the Paintbrush located on the tool palette next to the Hand to color either the graph pad page or the variables being displayed Just click and hold on the Paintbrush then select a color from the palette that appears Next click the page or variable to color it Another nice feature of the Graph Pad page is that by clicking and holding on a point on any curve line on the page the associated numerical value of the variable at that point in time will be dis
25. lates should be avoided whenever possible In fact it s worth paying a lot of attention to the visual presentation and neatness of map layout in general People won t be able to understand your story if it s written in sloppy penmanship Step 1 Rendering a Mental Model Numerating Once a first chunk of the map is rendered the second step numerating can unfold Numerating which includes clicking in equation logic where needed readies the model for computer simulation However before we embark upon the numeration process let s take a peek in the basement So far we ve been mapping out the plumbing of this simple ecosystem However beneath the surface of our neat little picture the software has been hard at work creating an equation infrastructure that we will need in order to simulate the system Let s take a look at what s been going on To do so click the down arrow located on the top of the left frame of the Map Model window just above the Globe icon Here s what you should see MM High Performance Systems Inc All rights reserved 10 7 Deer Population Deer Population t dt births deaths dt INIT Deer Population Place initial value here INF LOWS births Place righthand side of equation here OLUTFLOVWS ce deaths Place righthand side of equation here id birth fraction Place right hand side of equation here id death traction Place right h
26. lay This is the 6 icon from the right on the toolbar Click on it and deposit it on the screen then double click on the device Double click on the births flow to move it to the Selected List and use the pull down Increment list to change the increments displayed to no decimal points Click OK and voila you can see the numerical value for births at each point in time Now let s put down a device that will warn you when Vegetation the food supply is getting too high or too low Find the Warning Device icon on the toolbar it s the i from the right Plop it down on your screen and double click to open it Move Vegetation to the Selected List and whoa Lots of stuff comes at you Basically what MM High Performance Systems Inc All rights reserved 2 you re looking at is an apparatus for defining a normal cautionary panic range for the variable you ve entered In this case we ll assume that Vegetation values of 3000 to 4000 are normal 2000 to 3000 are cautionary and 0 to 2000 are bad or worthy of panic These numbers are selected to make the definition process easier we d need some more info to determine the actual numbers Begin by selecting the right high end of the scale box Type in 4000 Then into the low end left scale box type O Next select the far left zone by clicking once in the hollow elongated rectangle on the left side of the spectrum Make sure that it is the Panic zone i
27. n text sounds graphics and movies to each variable For now select the Text option Then click the Edit Text button Type in some text select a font size and click OK Then click on the second item in the selected list Repeat the process and OK your way out Then press the button and observe the unfurling When you click the dot in the middle of the element the text that you assigned will pop up MM High Performance Systems Inc All rights reserved 29 2 yourname stm Deer Population You can use the Text option in storytelling ta give a play by play description of the structure of your model Clicking the dot again will reveal the next piece of the model which will also have a dot on it In this way you can reveal the model a piece at a time providing end users with a multimedia play by play that will help them better understand the structure of the model In the deerA model we have used only text to annotate the description The STELLA Electronic Help files in the software will explain how to import graphics sounds and movies as well When you ve finished revealing the logic click the up arrow on the left frame of the window to return to the Interface level Next let s create a Control Panel Return to the Main Menu screen You should have a second button named Fly the System If you don t create one now Then find a blank screen to which you can navigate On this screen we ll cre
28. ndicated by the drop down menu titled Zone Type Make sure that the Zone begins at 0 and ends at 2000 Then click on the middle range making sure it is defined as Caution and make sure that the Zone begins at 2000 and ends at 3000 Then click the far right rectangle making sure it s the Normal zone and that zone begins at 3000 and ends at 4000 Make sure that the Show as Lamp option is checked and select the Lamp Size Large radio button If your dialog box looks like this Click OK to exit the dialog If it doesn t look like this make it so and then OK the dialog to exit s Te PAMARE ee ae Y E Phen n hf Show As Lamp 4000 one begins at 3000 Lamp Size Small Zone ends at 4000 Lamp CIEE Med f Lamp Size Large Bene Gite M Retain Ending Value Cancel Plop down another numeric display and move Vegetation to the Selected list Use the pull down Increment list to display no decimal points Click OK and yov ll have a numeric value for Vegetation to go along with your Warning Device Two more buttons and you ll be ready to fly First we ll create a navigation button that will take you back to the Main Menu Next we ll create a Run button Deposit a button and double click to open the dialog Select Menu under Button Purpose The default option is Run so click OK and you should have a button that says Run on your screen You may want to resize the button click once on the border to make the
29. ng cece deaths oot regenerating a birth fraction MM High Performance Systems Inc All rights reserved 31 Double click on birth fraction to move it into the Selected List You can choose to display the name value and navigation arrow or to create a small slider The Select Show Name and Show Values should be selected as the default option Then click on the Increment dropdown menu and choose how you want the numbers to be formatted Set the Min value to 0 and the Max value to 1 Then click OK Your slider should look like this birth fraction Now end users have the ability to adjust the birth fraction every time the simulation pauses Let s add another input device Select the Graphical Input Device GID from the Toolbar it s the 7 icon from the left Click once to deposit it then double click to open the dialog and double click on death fraction to move it to the Selected List Click OK Your GID should look like this The Graphical Input Device allows end users to change the effect that Vegetation has on death fraction without making them to go down to the Map Model level All they have to do is double click on the device and redraw the curve or input new data So now you have a graph a slider and GID We ll add a few more devices and you ll have a simple control panel Suppose you want to see how many births are occurring each year All you need to do is plop down a Numeric Disp
30. on As population rises it consumes vegetation more and more rapidly Eventually as vegetation runs out deaths will skyrocket Let s add vegetation to the model Round 3 Mapping Numerating and Simulating Click the close box to close the graph We now need to delete the connector between Deer Population and death fraction since we ve said it s Vegetation not Deer population that will now affect death fraction Deleting the connector requires some care Select the dynamite tool from the tool palette and click and hold on the small circle at the base of the connector that comes off of Deer Population Make sure that the connector not the stock is highlighted as indicated below Once you re certain you are dynamiting the correct building block release your click 2 yourname stm eo OAO EmA MRIN Xll Deer Population en een death fraction Add the necessary building blocks to the map to it look like this MM High Performance Systems Inc All rights reserved 2 Deer Population death fraction bith traction Vegetation consuming regenerating a T T 7 vegetation per deer regeneration per plant The map indicates that there are two links between Deer Population and Vegetation The first runs from Deer Population to consuming Vegetation will be consumed at ever increasing rates as deer population grows The second link is between Vegetation and deer death fraction In this case as V
31. ons In this case let s use Sensitivity Analysis to see if our model can generate overshoot and collapse Choose Sensi Specs from the Run Menu You will see the dialog shown here Allowable Selected Value C Deer Population O birth fraction O death fraction Variation Type Aunt Value f Aeremental of Buns f Gnstibutiorn md hac impar deta T M cenetivig in maph Print Setups Tale Cancel Double click on death fraction in the Allowable List to enter it into the Selected List Change the of Runs left side of the dialog box to 4 Then click on death fraction to select it in the Selected List Doing so activates the Variation Type selection Choose Incremental and enter a Start value of 02 and End value of 25 Click the Set button We are now set up to conduct 4 back to back simulations In run 1 the death fraction will be 02 in run 2 it will be 0967 in run 3 it will be 173 in run 4 it will be 25 The software has performed an interpolation to produce two points between the two extreme points you provided Next click the Graph button in the lower left corner of the dialog box This will cause anew page automatically set up to display multi run Sensitivity Analysis results to be created on a page within the Graph Pad that you have already created This page is a comparative graph Double click on Deer Population to move it to
32. oot and collapse Instead we ve generated a ubiquitous pattern in population dynamics S shaped growth To see the pattern more clearly you may wish to re scale Deer Population from 0 500 To yield S shaped growth we made death fraction increase as population increased You may want to experiment with different shaped graphical functions to see if you can generate the overshoot and collapse we ve been trying to produce No matter how hard you try you will not be able to make this system overshoot and collapse Let s take our rendering and simulating one step further to see how we can generate the behavior pattern we are looking for For Deer Population to fall deaths must exceed births For that to happen death fraction must exceed birth fraction Death fraction begins at a value less than birth fraction which is what allows the population to grow As the population grows death fraction rises and hence deaths rise At some point death fraction rises to equal birth fraction At that point births equal deaths and the Deer Population is constant And nothing can make it change because with population constant death fraction can t continue to increase The population is then locked in MM High Performance Systems Inc All rights reserved 21 steady state In order for death fraction to rise above birth fraction it must depend on something other than Deer Population For example consider making it depend on a food source vegetati
33. ou don t get it If you wish to include a variable in an equation you need to include that variable in the map Delete extra_deer_population from the equation and type or click the and click once on birth fraction The equation box should now read as follows Deer_Population birth_fraction Click OK to exit the dialog Note that there are no longer s on either the stock of Deer Population or the births flow Let s assume that for every 10 deer in the ecosystem two deer will be born every year Therefore the birth fraction in this system is 2 10 or 20 Double click on the birth fraction converter and type or click in the value of 20 Click OK to exit the dialog Fill in the remaining equations and inputs as follows deaths Deer_Population death_fraction death fraction 02 Your model should now be ready to simulate there should be no remaining in the map Step 2 Simulating In order to see the results of a simulation it s necessary to display them in graphical or tabular form The STELLA software provides many such options Here we ll use the Graph and Table Use Illustration 6 in the Appendix to create a graph pad on the Map Model level just plop the pad down anywhere and don t pushpin or lock it Then use Illustration 7 to enter Deer Population as the variable to be plotted Choose Run from the Run Menu You can also click once outside the boundaries of the graph clic
34. played underneath the variable name Try it you ll like it Let s now look at two other ways to display simulation output Click the close box to put away the Graph pad Then choose Model Prefs from the Model Menu The following dialog box will appear MM High Performance Systems Inc All rights reserved 16 Model Preferences Diagram Size Page Sequence Diagram Grid width fi TE G Bg width 20 pixels Height I pages r Height 50 pisels Total Pages Options Converters Animate Show pages f Large T Disable Posters gf sche M prabe map Drevin E M apague sub models W Division by Zero Alert Name Font Hide Foster Titles Mome hoes T Enforce Unit Consistency lM Hover to Show Numerical Values z Save Run Output to File ance Oox Note that in the dialog shown here the three building block icons under the word Animate have boxes around them By clicking each icon you too can make these boxes appear Do so now then OK the dialog box Click the forward button on your run controller and observe OK so this is not a very exciting animation at least not yet The only action is the stock of deer filling up Don t worry things will get more interesting Next use Illustrations 6 and 7 to create a table pad Enter Deer Population and other variables if you d like then run another simulation and watch the results They should look something like this Untitled
35. pulation Voila Overshoot and collapse You might want to compare your model to the deer1 model which can be found in the Getting Started Folder if you are having problems generating the results for example the scale of Deer Population has been changed MM High Performance Systems Inc All rights reserved 24 2 Untitled Ss 1 Deer Population 1 A0 E E Aai enna A En enra wS DAEA LOS EUNA porte 1 i M o 00 3 00 6 00 g 12 00 a ae Graph 1 p Untitled Time 2 27 Phi Tue Feb 01 2000 Can you explain why this behavior occurs As the Deer Population grows the food supply declines at an increasing rate This in turn causes the death fraction to grow Once the death fraction is greater than the birth fraction the population declines But since the population is high Vegetation continues to decrease You should create graphs and tables to examine other parts of the model particularly Vegetation so you can see the role vegetation decline plays in the collapse of deer population You could easily expand this model to include predators climatological effects or whatever your needs or interests dictate With a few name changes this model could apply to immigration into and out of a city or the spread of milfoil in a Northeastern lake The possibilities are limited only by your imagination Step 4 Communicating Now that you have produced a model that shows the results you want you have multipl
36. riate courses of action As you can see mental models are extremely important things Learning to construct mental models that better reflect the reality they seek to mimic and learning to simulate them more reliably are vital to making your world and our world work more effectively The aim of the STELLA software is to accelerate and enrich these learning processes The context for mastering the basics of the software will be the rendering simulating analyzing and communicating of a mental model of deer population dynamics Since we are seeking to build your basic expertise as quickly as possible we will keep the illustrative example simple By the time you complete the tutorial you should see many ways that you might extend the example to capture more aspects of the deer population dynamics Please feel free to do so The approach we will take in this tutorial will be to show you a picture and then ask you to perform the software operations or use the software features needed to produce the picture The operations themselves are illustrated using a progression of screen shot diagrams that depict the processes of rendering simulating analyzing and communicating The progression of diagrams appears in an Appendix that begins on p 35 The Context Population dynamics is a key content area in many social and physical science curricula From one celled organisms to human populations a generic structure can be used as a basis for studyin
37. rths per time period depends on Deer Population since an increase in the number of deer will cause an increase in deer births To show that dependency we ll use a connector to connect the Stock to the inflow Follow the directions in Illustration 4 in the Appendix to do this Then follow the instructions in Illustration 1 to deposit a converter and connect it to the births flow as well You should then have a diagram that looks like this Deer Population births birth fraction This picture says the population of deer generates the inflow of births The birth fraction tells how many offspring are produced per year per deer Before we simulate this chunk of the model let s add deaths to the picture Add a deaths outflow see Illustration 2 in the Appendix for help and a death fraction Use connectors to complete the map which should look like this MM High Performance Systems Inc All rights reserved 9 Deer Population births deaths birth fraction death traction By adding the deaths structure we re saying that some fraction of the population dies each year Take a few moments to experiment with moving the nameplates on each of the different objects on your map We strongly urge you to shift these nameplates around when creating maps in order to prevent wires connectors from violating nameplates Because an explicit purpose of a STELLA map is to communicate a clear picture wires running through namep
38. s your STELLA Getting Started experience We hope it has given you a sense of the incredible power of this highly versatile software tool If you have any comments or questions please contact us via e mail fax or phone We d love to hear from you e mail support hps inc co phone 603 643 9636 or 800 332 1202 fax 603 643 9502 website http www hps inc com MM High Performance Systems Inc All rights reserved 35 Appendix Basic Software Operations amp Features Rendering Illustration 1 Depositing Naming amp Re positioning Stocks amp Converters and Nameplates 4 STELLA Research 6 0 OSG OBO fm A PEF i a gt Step 1 Click to selectthe stock or converter Step 2 Position your cursor on the screen where you want to depoasitthe stock or converter Noname Deer Population Step 4 Mame the stock or converter by typing to replace the Noname designation a Step 5 To re position the stock or converter click and hoald on it then drag itto the new position Step 3 Click to make the deposit Step 6 To re position a nameplate click and hold on it then drag itto the desired location MM High Performance Systems Inc All rights reserved 36 Illustration 2 Hooking up Flows olsO omo ei A PEE aa Step 1 Click the flow icon the second building block located nestto the stock Step 2 Click and hold then drag the flow cursor until you achieve the desired
39. screen Use the Text Box see Illustration 8 in the appendix to say something to welcome people to your simulation based learning environment Here s what we chose Welcome to DEER DYNAMICS In addition to making use of the text box we imported a graphic into the Graphics Frame If you want to do the latter select the graphics frame from the palette Click to deposit it Then double click anywhere on its border to open the dialog Importing graphics is straightforward once you re inside the dialog We ve saved you the graphic we used in case you want to use it Its called deer pct and it can be found in the graphics folder within the Getting Started Folder Just click From File and press the Import Picture MM High Performance Systems Inc All rights reserved 26 button Navigate to the deer pct file found in your Graphics folder contained within the Getting Started with STELLA folder and click Open Then click OK to exit the dialog box The next addition to the Welcome screen will be a navigation button that when clicked will transport us to a menu screen Before going there though let s explore the functions of the button Find the button on the tool palette 2 yourname stm The multi purpose Button Select it and then deposit it in the lower left of your screen Double click on the border of the button the cursor will change to an arrow when you are in the right place and then double click to open the
40. served 12 LJ Deer Population f Reservoir C Conveyor E ewe C Oven M Nor negative Array Allowable Inputs dee births e deaths EBEE ECEE iP birth fraction Fi death fraction EVelelely BERERE i e C JINITIAL D eer _Fopulation Units Place initial value here Document Message Cancel The first thing to note is that if you have the Basic version of the STELLA software the radio buttons for creating either a Queue or Oven do not appear at the top of your dialog box No need to fret These elements are useful primarily in specialized technical applications Moving down the dialog box ignore the Allowable Inputs list for now It becomes useful in more advanced applications when you wish to construct an initial value equation rather than using a number to initialize your stock The calculator keypad to right of the list is useful for clicking in numerical values We ll use it in a moment Another point of interest in the dialog is the Units button located on the right just above the initial value box Units are explained in the Electronic Help Files Along the bottom of the dialog are four buttons The last two Cancel and OK should require no explanation The Document button when clicked pops up a space into which you can type text that describes your assumptions documents the source of numerical information etc Finally the Me
41. sh to make the first bend Stop dragging then depress the Shit key to To re size a segment make the bend Continue dragging to of pipe click the flow the next point where you wish to bend regulator to reveal the pipe again depress the shift key re sizing handles and so on Then click and hold a handle and drag to A Stack caus re size KORG k a flow a flow a bent flow To reverse the direction of flow depress and hold the Ctrl key Option key on Macintosh then position the index finger of the Hand cursor Inside the arrowhead and click MM High Performance Systems Inc All rights reserved 38 Illustration 4 Hooking up and Re positioning Connectors O 0h Of MA MEFs Step 1 Click to select the connector Honame 4 otep 2 Position the connectar cursor within t the stock fow regulator or converter A stock Step 3 Click and hold then drag the connector to the target converter or flow regulator When the connector hits its u target the target will highlight Release vour click the connection is forged Step 4 To re positian the connector so that it traces a different arc click and hold on the takeoff button fatthe base ofthe connector and slide it around the perimeter of the building block from which the connector is a converter a converter emanating MOTE Connectors cannot connecti TO stocks only flows can connectinto stocks Connectors can connect out from stocks i
42. ssage button will let you instruct the variable to post some sort of a message play a movie or sound navigate to a new screen post a text message We ll examine this feature in the Communicating section of the tutorial OK back to the keypad Use it or your keyboard to enter the value 100 into the equation box By doing so you are stating that there is an initial value of 100 deer in the Deer Population stock This value as the dialog indicates is only an initial value for Deer Population Once the simulation starts new values for the stock will be calculated for each instant in time or each dt in this model dt is set to its default value of 25 the MM High Performance Systems Inc All rights reserved 13 simulation will make calculations each 1 4 of a time period which is in this model a month Once the 100 is entered click OK to exit the dialog Next we ll define the births flow Double click the births flow regulator Here s what you should see ome births f UNIFLOW C BIFLOD m nt conversion Hy pe C Deer Population EEHEHE F birth_fractior Al 5 6 7 342 3 _ _o ffs lel om births Place right hand side of equation here Become Graph Document Message Cancel o At the top of the dialog you have the option to make the flow a uniflow or biflow Biflows allow flow to occur in either direction both into or out of the stock
43. t both the X and Y axes have been re scaled from their default 0 100 values Next an upward sloping curve has been traced through the range meaning that the higher the deer population the higher the death fraction A quick note about graphical functions they do not extrapolate What this means is that even 1f the Deer MM High Performance Systems Inc All rights reserved 20 Population goes above 500 the death fraction in our illustrative graphical function will remain at 805 the maximum value defined by the graphical function Click OK to exit the graphical function dialog Your map should now be free of s and a tiny squiggle should appear in the death fraction converter indicating that this value is now a graphical function Before we run again and see the results of this change we must first turn off Sensitivity Analysis Choose Sensi Specs from the Run Menu You will get a message telling you that the current setup has been changed Click OK then click Cancel in the resulting dialog box Then double click on the graph pad icon to view the graph and run You should see this on your graph i Untitled Ss 1 Deer Population 1 1500 POD noon onoponenoanoooo ee hoodoo E a a a A E A EE E Dano pa t mna aA RA KARD 0 00 3 D 6 00 4 00 12 00 aes Graph 1 p2 Untitled Time 2 49 PM Tue Feb 01 2000 y Deer Population no longer grows forever However we have yet to achieve oversh
44. the Selected List MM High Performance Systems Inc All rights reserved 18 Set the scale of Deer Population to run from 0 to 500 see Appendix 7 for instructions Click OK to exit the dialog Choose S Run from the Run Menu or click the Forward button on your run controller and observe as the software automatically performs four runs of the model each with a progressively larger death fraction If you d like to see the value of death fraction associated with each of the four curves click the in the lower left corner of the graph pad page After you ve formatted Deer Population removing the decimal points it should look like this S Untitled Ss 1 Deer Population 2 Deer Population 3 Deer Population 4 Deer Population il S00 i 0 0 00 3 00 6 00 9 00 12 00 Ja BF Graph 1 p2 Untitled Time B 07 PM Tue Feb 15 2000 7 OK Still no overshoot and collapse However note that the model generates a decline in deer population run 4 when death fraction is greater than birth fraction When birth fraction is greater than death fraction runs 1 3 population grows So right now our model can either grow forever or decline forever based on which fraction is bigger But it can t grow then decline To get overshoot and collapse we need some way to make death fraction become greater than death fraction during the run We need to add some relationships to make this happen In using the softwar
45. ware associated with 1 rendering a mental model 2 simulating the model to yield dynamic outputs 3 analyzing the outputs to understand what s causing them and what you might do to change them and 4 communicating your understanding by making the insights derivable from the model available for discovery by others This tutorial is designed for users of both the STELLA Basic and Research versions of the software The Research version was used to develop this tutorial Those owning the Basic version might see some slightly different screen shots than the ones appearing in the tutorial Differences between the two versions will be identified as they arise The Basics will take you about an hour to complete The tutorial is divided into sections so that if you choose to take a break and return later to complete the tutorial no problem Have fun Be cool it would be hard not to after mastering the basics of this software Stay systemic MM High Performance Systems Inc All rights reserved 3 The Basics A Tutorial for New Users The STELLA software is designed to increase the effectiveness of the set of processes by which we render simulate analyze and communicate our mental models Mental models are those things we all necessarily carry around in our heads that help us to 1 make meaning out of what we experience 2 share and evolve that meaning by communicating with others and 3 evaluate and decide upon approp
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