Forrester’s Limits To Growth Model For Your Personal Computer

Posted by James Bowery on Thursday, 31 May 2007 02:16.

We’ve all heard about the “Limits to Growth”. Well, the results of the computer program that started it all are published in “World Dynamics” by Jay W. Forrester (The MIT Press, Cambridge, MA, 1971; second edition, 1973). Back then you had to be at an institution to run the computer program to simulate the future world dynamics, so modeled. Nowadays you can run it on your own personal computer and play around with the model all you want (after spending a day or two going through the tutorials). All you need to do is download Vensim PLE (take care to download all files first to a known location like your “Desktop” so you can direct the installer program to them when it asks you for their location), and then open the WORLD.MDL file most likely located at: C:\Program Files\Vensim\models\sample\EXTRA\WORLD.MDL

Read on for some screen shots of the output.

PS: Meadows et al’s 2003 update to the original model is in the file WRLD3-03.VMF, most likely located at C:\Program Files\Vensim\models\sample\WRLD3-03\WRLD3-03.VMF

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Comments:

Posted by President Barbicane on Thu, 31 May 2007 06:31 | #

Are there any testable predictions in the world model?

Posted by James Bowery on Thu, 31 May 2007 07:25 | #

The graphs of curves of various quantities vs time are the predictions.

Posted by James Bowery on Thu, 31 May 2007 14:54 | #

When you say “error terms” are you referring to the numerical methods used to run the differential equations or to something about the exponential propagation of input uncertainty?

Posted by Frank McGuckin on Thu, 31 May 2007 18:14 | #

The late Donella Meadows was a fanatical multiculturalist who for the most part supported open borders. What a piece of shit.

There is no environmental movement in the US.

Go to Wildlands website. I made a post there. If Dave Foreman has his way, White Americans will nothave the option of running away from non-whites much longer. And this would be good, for once the froniter is closed to White Americans, a race war will start which is the only way White Americans can prevent their racial dispossesson in America.

Posted by SDLEE on Tue, 31 Aug 2010 17:51 | #

>>Sorry, to be clear, the rounding error caused at each year the projection extended further—the >>computer rounded everything and produced a “right answer plus epsilon” for the next year. Then the >>epsilon was included in the input for the iteration for the following year, and after 30-40 iterations >>the exponential functions in the equations caused it to explode off the screen.

This (rounding error) is an artifact of using digital computer in solving “any” ordinary differential equation, not the “world dynamics.” The mathmatics of the ‘world dynamics” is called “ordinary differential equation” Reduce the delta (DT) with “Runge-Kutta 4” then, the rounding error can be reduced considerable so that we don’t need to worry about the rounding error anymore. See Dr. Moler’s book at Matlab (available free). Advancements in “numerical anaysis” and computer make the rounding error as of little concern.

SDLEE

Posted by SDLEE on Fri, 23 Sep 2011 16:14 | #

Dr. Cleve Molder’s free e-books on numerical analysis and MATLAB. He is one of the founder of the Matlab and world-renowned numerical analyst.

http://www.mathworks.com/moler/index.html

Almost all engineering analyses and models especially for dynamic system are to solve “differential equations” such as the famous Newton’s law (sum of F=M*a=M*d(velocity)/dt, where velocity = d(displacement)/dt). Some examples are structural dynamics (such as bending shape of a skyscraper, bridge, and car, etc.). Computer-Aided-Engineering (CAE) is entirely based on differential equations (called finite element analysis (FEA)). Rounding error is a serious issue in computer analysis and due attention should be paid. However, rounding error is nothing to do with the World Model.

Posted by PattiMichelle on Tue, 23 Apr 2013 01:54 | #

It’s amazing that people find issue with these models. They are being run even now, and, basically, there is no way to avert disaster. There is no charlatanism here. This is standard science that anyone with a decent degree could do themselves. And it’s being done all the time. It was only really cutting-edge in the 70’s. Now it’s business as usual. Except the clear outcomes are all anti-capitalizm (i.e., the Tragedy Of The Commons). Nobody knows how to avoid this in the long term. The results of the models simply show you how it happens, and give you and idea of what you can change to slightly modify the outcomes. (Like reinforcing the levies in New Orleans, which we didn’t bother to do.) So, yes, we are heading for catastrophe for most people in my lifetime, but (mostly) not for the ruling elites.

It’s really not the model, per se, but the *way* of seeing the world through the lens of knowing about interconnecting systems, which you *can* model accurately - this is the real insight in the LTG work and Donella/Dennis Meadow’s work. Literally, they *proved* that humans are an “outbreak” - just like every other population on the planet, and follow the same exponential growth -> collapse - unless we do something intelligent, which we have not.

Patricia,
Research Scientist

Posted by Emhwan Kim(@ASSIST) on Sun, 03 Jun 2018 01:30 | #

Is there any update of this?

Posted by Tomasina on Wed, 13 Feb 2019 00:53 | #

No updates beyond the usual political bullshit. The original Sim City has more pedictive power and actual science behind it than any of these “models”.