[From Bruce Abbott (2016.11.19.1415 EST)]
My thanks to Chad and Fred for providing the notice of Jay W. Forrester’s death. I have two of Forrester’s books on my bookshelf: Industrial Dynamics (1962) and a “second preliminary edition” of Principles of Systems (1968, 1973). Those books contain a lot of useful information about modeling dynamic systems (which includes control systems) in terms of “levels” and “flows.” Levels are accumulations, like the level of water in a tank to which water is being added, and flows are the rates of input or output to/from levels. Together with “sources” and “sinks,” the lines connecting the elements, and “valves” that alter the flow rates, these elements are sufficient to build dynamic systems of considerable complexity.
These elements are employed in an application called “Vensim,” which provides a graphical user interface onto which one can plunk down the various elements as graphic icons and connect them to form the system being modeled. After adding parameters and functions to the elements, you can run the model and see how it behaves.
Some years ago, Fred Nickols distributed a limited number of copies of Vensim free of charge and I was one of those who received one, which I still have installed on my old laptop. When fitting parameters to a control-system model, Bill Powers found that Vensim did a better job of fitting than the simple method he used for this purpose in his programs.
Ventana Systems, the maker of Vensim, is offering a home version (Vensim PLE) for $50 and a more capable but still limited version for $169. Through December they are also offering a 20% discount, so any modelers out there might want to take advantage of this low pricing while it lasts.
[From Chad Green (2016.11.18.0911 EDT)]
Jay W. Forrester Dies at 98; a Pioneer in Computer Models
From: Fred Nickols [mailto:email@example.com]
Sent: Friday, November 18, 2016 1:06 PM
Subject: Jay Forrester
Jay Forrester has passed away. He was 98. Here’s a snippet from a notice I received from the Systems Dynamics Society.
It is with great sadness that we are writing to you to announce that Jay W. Forrester, Professor of Management Emeritus at MIT, has died at the age of 98.
A full obituary is now available in the New York Times. Further information is available via the System Dynamics Society homepage.