I’ve just been looking into replicating the DICE-2007 model in Vensim (as I’ve previously done with DICE and RICE). As usual, it’s in GAMS, which is very powerful for optimization and general equilibrium work. However, it has to be the most horrible language I’ve ever seen for specifying dynamic models – worse than Excel, BASIC, you name it. The only contender for the title of time series horror show I can think of is SQL. I was recently amused when a GAMS user in China, working with a complex, unfinished Vensim model, heavy on arrays and interface detail, 50x the size of DICE, exclaimed, “it’s so easy!” I’d rather go to the dentist than plow through yet another pile of GAMS code to figure out what gsig(T)=gsigma*EXP(-dsig*10*(ORD(T)-1)-dsig2*10*((ord(t)-1)**2));sigma(“1”)=sig0;LOOP(T,sigma(T+1)=(sigma(T)/((1-gsig(T+1))));); means. End rant.
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Don't just do something, stand there! Reflections on the counterintuitive behavior of complex systems, seen through the eyes of System Dynamics, Systems Thinking and simulation.