Ventana software support forum

Hi all

I have a (hopefully) quick question.

What optimisation method does VenSim use, i.e. what is the value that is being optimised, e.g. residual sum of squares, etc.

I couldn't seem to find it in the manuals

Cheers

Mik

Vensim uses a modifies Powell search. The book numerical recipes in C has a good description of this as do numerous other texts.

It sounds to me like you're actually asking about the objective function.

In a calibration optimization, it is the sum of squared residuals, by whatever weights you select. (If you're using Kalman filtering, it's the log likelihood, more complex but same general idea).

In a policy optimization, it's the simple sum of whatever variables you specify, again with your selected weights.

You can use a policy payoff to do things like robust estimation, where you define a variable
error = ABS(data - model)
and use that for the payoff.

Both kinds of payoffs integrate over the whole period of the simulation, so if you want to consider only the final value of something, you can create an added variable, like
payoffVar = modelVar*PULSE(FINAL TIME,TIME STEP)
i.e. something that returns 0 except at FINAL TIME.

Tom

Thanks Tom and Bob

I was asking about the objective function - I couldn't think of the right term.

Cheers

Mik