REPLY In-simulation linear programming (SD7212)

[SDMAIL Gonenc Yucel]

Posted by  Gonenc Yucel <g.yucel at tudelft.nl>

Hi Hazhir,
Let me see if I get it properly.

For example you want to model a supply chain, in which actors use some sort of
optimal lot size policy. And periodically, they stop and consider their optimal
lot sizes by solving a LP-problem based on market conditions. Then continue with
this new lot size. 
Is this somehow similar to what you want to do?

If so, I can think of two options in terms of implementation.
One of them is coupling Vensim with Matlab or a Java program using its DLL. In
this option you set the decision variables as "Gaming variables" in Vensim.
External code controls the Vensim in terms of how long to run and when to pause
for new input for gaming variables. Then you may get some variable values from
the simulation. Solve the LP in the external code, and then pass the new
parameter values to Vensim. After that point on Vensim will continue running
with
these new values. I don't exactly know, but I assume there should be some
libraries for solving basic LP formulations in Java. Probably Bob will correct
me
if I say anything wrong here.

Details of how to do this are well explained in Vensim manual. Once I did
something similar just for experimental purposes (a java code that pauses the
Vensim run, getting some values from the simulation and changing some
parameters). If you think it might help, I may send it as well.

Second option would be transfering the model to MatLab platform. And then
manipulating the run as you wish. If the model is modest in size, this is a
clean
option. It comes with the advantage of having access to optimization, analysis
and visualization facilities of MatLab.

Hope it helps a bit.

regards,
gonenc
Posted by  Gonenc Yucel <g.yucel at tudelft.nl>
posting date  Tue, 29 Jul 2008 14:18:53 +0200