About

Welcome. You can read some background here, or go straight to the models.

I’m gradually porting my existing Model Library to here. This site replaces my experimental modelwiki – the wiki format just wasn’t working for me. Hopefully this will be a more permanent home.

This library contains replications of many classic models from system dynamics and related fields. Citations are provided. Unfortunately I don’t know of online resources for most of the articles, but links are provided where possible. MIT theses are now available online through MIT Document Services. Many classic SD publications are available through Pegasus Communications and Amazon.

Many of the models in this library were recreated from published works by students in the MIT Sloan School’s PhD Seminar in System Dynamics. Where credit is unknown, thanks should go to Rogelio Oliva, Scott Rockart, Nelson Repenning, Ed Anderson, Liz Krahmer, Hank Taylor, and several other MIT students for the arduous process of reconstructing these models from published sources. Be forewarned that, since most of these models are replications, it’s possible that they contain errors introduced in the publication or reconstruction process.

Generally, the models in this library may be freely used and distributed, subject to authors’ copyright, which should be noted in the model file. Naturally you should acknowledge the hard work of the authors and implementors who created these files.

There are some differences in floating point math between hardware platforms, so you may find differences in output or fp errors I haven’t discovered that occur only on one platform. You may need to translate carriage returns and linefeeds to your platform’s standard before using text .mdl files. Many models can be run and edited with Vensim PLE (free); models with arrays, optimization, or other advanced features may be browsed and run with the Vensim Model Reader, but require purchase of Vensim DSS or Pro for editing.

Submission Guidelines

I’m always thrilled to have new replications of classic models and useful model components. Because I can’t effectively curate other formats, I’m  standardizing on Vensim 5.x file formats for contributions to this library. Vensim files may be submitted in .vmf, .mdl, .vpm, and .vpa format. Models that use auxiliary files (.cin, .xls, .vdf, etc.) should use published model format (.vpm) or be placed in a .zip archive.

To submit a model:

Be sure you have permission from the copyright holder, or that the model is in the public domain.

Use the template below to create a new page for your model (improve the template as needed).

If possible, add an abstract, pretty pictures, etc. to indicate what the model is about. Provide .pdf papers or link to external sites to provide background.

I may eventually enable user registration here, but for now, email submissions to me:

Requirements

An ideal model will observe the following guidelines:

   * Vensim or another standard modeling package format (any version; preferably no external function library dependencies)
   * Clean diagram (hopefully with views corresponding to published diagrams)
   * Clean variable names (if original uses short names, append clear names at the end, e.g., "DCD" becomes "DCD Developer Cost of Disposal"
   * Documentation wherever equations are not self-explanatory
   * Numerically correct (replicates published results, or documents discrepancies)
   * Custom graphs predefined where useful
   * Command scripts, changes files, or other means to automate scenario/experiment replication
   * Units balance
   * Title page in the model, with source attribution, license information (if any), a link to this library, etc.

For Vensim models, it’s a good idea to include a PLE-compatible binary (.vmf), or a published model (.vpm) for use with the Vensim Model Reader.

Template

Model Name: BANANA

Citation: J.P. Modeler (2005) Dynamics of Fruit. Journal of Nonlinear Agriculture 8:3, pg. 801-805

Source: ????

Copyright: J.P. Modeler (2005)

License: Gnu GPL

Replicated by: I.M. Gradstudent, 2008

Peer reviewed: Yes

Units balance: Yes

Format: Vensim

Target audience: Orchard managers

Questions answered: Should managers spray for medflies? Which came first, the apple, or the worm?

Software: Vensim

Notes: Discussion, images, etc.

One thought on “About

  1. Roya Farhadi

    Dear Tom
    I am Roya Farhadi, PhD scholar of Tehran university of entomology. My thesis is about prey and predator. I would like to develop a vensim model. As I surfed in net, I found a vensim model figured in your belog (http://models.metasd.com/wp-content/uploads/2013/04/Structure.png).

    I would like to know how has developed this model and how can I contact her or him?
    I would appreciate you for the time you spend for me.

    Best regards,
    Roya Farhadi

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