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Type in "deaths".Ĭlick on the Converter tool, then click above deaths, and type in "reference", press the enter key, and type in "lifetime". This time we get more interesting behavior:īy clicking on the circle above birth rate, you can spin the dial to see what happens as the birth rate changes.Ĭlick on the Flow tool ( or ), then press the mouse button down on the rectangle below Population, drag the mouse to the right, and release the mouse button. Note that units are already filled in - this is done automatically for flows based on the stock they're connected to.Ĭlick on the Run button in the Run toolbar at the bottom of the program. You can also simply type in this equation (as you do so, an autocomplete will appear). You can also click on any of the names and reposition them relative to their corresponding shape (circle or rectangle) by dragging them, if you want to create a more pleasing diagram.Ĭlick on births, and, in the equation panel at the right, click on Population in the list toward the top, then the * button in the Operators list, then birth rate in the same list Population is in. You should end up with a diagram that looks like this: Select the small handles at the beginning of each of the flows you've just created in order to change the shape of the connectors. In the equation panel at the right, enter 0.05 for the equation and Per Month for units.Ĭlick on the Connector tool, then press the mouse button down on the circle above birth rate, drag the mouse to the circle above births, and let go.Ĭlick on the Connector tool again, then press the mouse button down on the rectangle below Population, drag the mouse to the circle above births, and let go. To define it, we first need to add additional structure.Ĭlick on the Converter tool, then click above births, and type in "birth rate".
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The small caution sign indicates that births hasn't yet been defined. With nothing to change Population, it simply remains constant at 25.Ĭlick on the Flow tool ( or ), then press the mouse button down to the left of Population, drag the mouse until it's over the rectangle for population, and release the mouse button.
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After you do that, you'll see that Population has a small graph inside of it: In the equation box, type in 25, and in the Units box, type in Critters (or Frogs, or Rabbits, or any other species you'd like).Ĭlick on the Run button in the Run toolbar at the bottom of the program. Type in "Population" where the stock uses the default name (Stock 1).Ĭlick on at the bottom of the panel, and you'll see the equation panel: Our main, and only, stock is population, and putting down stocks is almost always the best way to get started building models.Ĭlick on the Stock tool ( or ) on the Build toolbar at the top, then click in the upper middle part of the white area below. As we progress, we'll fill in a few of the details around this formulation to make the complete model. While planning out a model normally takes significant time and thought, in this case we'll jump to a very simple structure: essentially just population, births, deaths, and an effect from crowding. We want to model population growth in the face of a limited carrying capacity. Make sure that Start Time is 0 and DT is 1/4, with Fractional checked (normally these will already be this way). In the panel to the right, change the Stop Time to 100. If you have Stella Architect, and are in the interface window, go to the model window (select Open Model window from the Window menu, or click on in the Build toolbar).
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If you have Stella Professional, start it. It doesn't matter which you use for this model. Note that, depending on your selection when you first started the software, you may get Stock or Non-Negative Stock and Biflow or Flow in the toolbar.
If statement in stella architect software#
It's intended as a quick introduction to using the modeling software with step by step instructions. In this tutorial, we'll walk through the mechanics of building a simple population model. Model Building Tutorial Model Building Tutorial