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DYNAMOI was surprised to see that DYNAMO hasn't been mentioned here in the past. DYNAMO (DYNAmic MOdels) was the simulation language used to code the simulations that led to the famous 1972 book The Limits to Growth from The Club of Rome. The language was designed in the late 1950s. It is clear that the language was used in several other places and evolved through several iterations, though I am not sure how extensively it was used. When Stafford Beer was creating Cybersyn for Salvador Allende he used DYNAMO to save time suggesting it was somewhat of a standard tool (this is described in Andrew Pickering's important book The Cybernetic Brain). The language itself is essentially what you'd expect. It is declarative, programs consisting of a set of equations. The equations are zero and firstorder difference equations of two kinds: level equations (accumulations) and rate equations (flows). Computation is integration over time. Levels can depend on rates and vice versa with the language automatically handling dependencies and circularities. Code looks like code looked those days: fixed columns, all caps, eight characters identifiers. Here are a few links:

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