Put the animals onto the X axis and new_animal flow onto the Y axis.Ģ. Double click on the Y-axis and select "scatter" as the graph type. Create another graph on the same page as the model and number+flow vs. In what regions does positive feedback dominate and in what regions does negative feedback dominate?ġ. What are the starting points, why is one high in the middle, what is the slope of the growth curveħ. run the model and adjust the time, growth rate and carrying capacity until you get the characteristic sigmoidal curveĭouble click on the Y-axis and send over the flow of new animalsīe able to explain in detail all the features of the flow and stock change the flow equation to the "Logistic" model -Īnimals * growth_rate * (carrying_capacity - animals)/carrying_capacityĤ. put a value of 1000 in that as an example starting pointģ. Then draw a connection to "new geese" flow rate controller.Ģ. Modify your current exponential growth model by adding a new convertor and label it "carrying capacity". Negative feedback - the "Logistic" equationġ. You designed the model, you need to be able to describe all features.īefore proceeding to section B, please answer question 1 on your handout.ī. Observe and be able to describe every feature of the output. New animal flow =animals*animal_growth_rateīefore you do anything else - click on the pin in the upper left corner to pin it downĭouble click on the Y-axis and select animals and then "send" that over to the plottingġ3. Enter the appropriate starting values of equations by double clicking on the icon which will open a dialog box. Start by toggling the STELLA window from the "map" mode to the "equation" mode.ĩ. Now you need to add values and equations to this diagram. Your diagram/map should look like this:Ĩ. But the stock of animals is the number or amount, not actual animals.ħ. That makes more intuitive sense if the stock is water or carbon than with animals. This is because information can't flow to a stock. Try if you like to go the other way, STELLA won't let you. Create an information links from the stock to the flow valve control and from the convertor to the flow valve. This will hold the constant growth rate that is used to determine the flow of new animals into the stock.Ħ. Create a convertor and name it something like "animal growth rate". Select the "dynamite" icon, move you mouse over the offending icon and blow that baby up! This program would even be better with sound effects.ĥ. Removing connections and icons in STELLA is satisfying and therapeutic.
If there is a cloud underneath, it didn't connect. You can test this by selecting the stock and moving it a bit. You should have a cloud (source) at one end and the flow should be connected at the other end. Move your mouse to the left of the stock a couple inches, click and hold down while you drag toward the stock and don't release until the mouse pointer is in the box. Name this stock "animals" (or any growing organism you choose).ģ. Click on the stock icon, move your mouse to the page and click again. Constant ratio - Exponential growth modelĢ. I made this page narrow so that you can have the tutorial window open off to the side of a STELLA page.Īt the end of this assignment, you will be asked to print a model that you made and answer a question by writing on that page.Ī. Exercise 3: Growth Models - STELLA tutorial
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