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
Optimization procedure
-
- Senior Member
- Posts: 1107
- Joined: Wed Mar 12, 2003 2:46 pm
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
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
/*
Advice to posters (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Blog: http://blog.metasd.com
Model library: http://models.metasd.com
Bookmarks: http://delicious.com/tomfid/SystemDynamics
*/
Advice to posters (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Blog: http://blog.metasd.com
Model library: http://models.metasd.com
Bookmarks: http://delicious.com/tomfid/SystemDynamics
*/