This program lets you construct and run mathematical models using a very easy to understand graphical interface. For each element in your model, you make a box on the screen. Inside that box, you put the starting amount of that element. Then you use the mouse to draw arrows between the boxes representing flows of stuff from one box to another, or effects of one box on another. For each arrow, you type in an ordinary differential equation which specifies what that arrow does. For instance, to model growth of a tree, you might have a tree box, a sunlight box and a CO2 box, and arrows coming from the sunlight and the CO2 into the tree. The tree would start out with a certain mass, and the sunlight and CO2 could each be given appropriate starting values and changes over time (e.g. you could put the sun on a 24 hour cycle by modelling it with a sine wave) and you would have some equation like dTree/dt = function(sunlight, CO2) associated with the arrows. Then you could run this model and watch the tree grow. The growth of the tree would be represented both by the tree box filling up, and you can also make graphs of any of the variables over time.

This program is really nicely designed for teaching. The learning curve is quite small, and even though the equations are not hidden from the user, the interface makes the mathematics behind the models quite transparent. Yet the mathematics is still rigorous, and once students learn to use this tool they can use it for high quality work (plenty of researches use Stella as well). Instructors could also use this program to set up models ahead of time which the students could then play with, though if one of the other programs mentioned in this FAQ does that model, its probably better to use the special program. I think Stella should be useful from advanced undergraduate level courses where modelling is discussed all the way through graduate level courses. One warning is that (as with any mathematical programs) the instructor should probably know something about numerical solution techniques if you do not want to get into trouble.

Computer: Macintosh (and Windows ?).

Source: High Performance Software

Cost: Low (ask for educational pricing)

Last update 22nd of January 1996