QUERY Teaching Causal Loops to Simulation

[Jason Foster <jason.foster@ut]

Posted by Jason Foster <jason.foster@utoronto.ca>

I will be incorporating some systems dynamics modeling into my upcoming engineering design course and am looking for some freely- available, fully functional tools for my students to learn. Given that my students all have access to Microsoft Office or OpenOffice they do have access to a spreadsheet, but I have yet to find any discussions detailing the transition from a causal loop diagram to a spreadsheet and then to simulation outputs.

The models that I intend to have the students develop should be sufficiently large that a size-limited tool would be problematic, and the students would lynch me if they couldn't save their models and come back to them. In theory the students could run the free Stella under a virtualization tool and use virtual machine snapshots to simulate saving, but that goes against the spirit of the free tool.

Ideally I would go with something along the lines of Matlab/Octave or a similar mathematically-oriented approach so that the students can develop a better understanding of how these systems are being simulated (e.g. what kind of numerical representations and algorithms are being used) as opposed to becoming only adept users of the software. Again, my quick scan has not identified a textbook that explains (in gory detail) how to go from causal loop diagram through to systems of differential equations through to solution. I have a vague memory of seeing someone use Simulink to draw a CLD and the Matlab to solve it, but I have no concrete materials.

In all likelihood there is such a textbook (or online example) that to this point I have not found. If anyone can point me in an appropriate direction, that would be great. Whatever slides, tutorial materials, and examples I develop will be made available under a Creative Commons license.

Thanks to everyone for your help!

Jason Foster
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Lecturer in Engineering Design Education, Division of Engineering Science University of Toronto Posted by Jason Foster <jason.foster@utoronto.ca> posting date Fri, 24 Aug 2007 09:16:42 -0400 _______________________________________________

[""Zagonel-Santos, Aldo A"" <a]

Posted by ""Zagonel-Santos, Aldo A"" <aazagon@sandia.gov>

You should take a look at Exposé. It bridges spreadsheet-based models and SD-like diagrams, ""exposing"" the overall causal structure of the spreadsheet-based model, including its feedbacks and accumulations:

http://www.attunegroup.com/Expose/Summa ... atures.pdf

It was developed by Mohammad Mojtahedzadeh
(mohammad@attunegroup.com)

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Posted by ""Zagonel-Santos, Aldo A"" <aazagon@sandia.gov> posting date Sat, 25 Aug 2007 09:40:11 -0600 _______________________________________________

[John Sterman <jsterman@MIT.ED]

Posted by John Sterman <jsterman@MIT.EDU>

I would recommend VensimPLE. VensimPLE is excellent for diagramming, including causal diagrams without stock and flow structure, stock and flow diagrams, and full diagrams that integrate the stock-flow and feedback structure. It also supports simulation, has no effective limit on model size (for student type models) and you can save your work. Best of all, it is free for student use, and largely for that reason, we use it in our system dynamics classes at MIT. FYI, the syllabus, lecture schedule, and assignments for our introductory system dynamics class are all available online through MIT's Open CourseWare project. See

http://ocw.mit.edu/OcwWeb/Sloan-School-of- Management/15-874Fall2003/CourseHome/index.htm.

You should also examine Powersim and iThink -- both are also excellent but, as far as I know, are not available at no cost for students in a fully functional form with no size or save restrictions (I trust that if this is wrong I will be promptly corrected).

As for textbooks, see

Sterman, Business Dynamics
John Morecroft's new book
Kim Warren's text on strategy applications Cavana and Maani

and a number of others.

Good luck!

John Sterman
Posted by John Sterman <jsterman@MIT.EDU> posting date Sun, 26 Aug 2007 16:38:41 -0400 _______________________________________________