Can you help me with multiple allocation?

[Marga]

Hello,

I'm trying to program a multiple source-multiple sink allocation in Vensim, a sort of market with many products and many consumers and all the posibilities of interchange between them.

I have tryed with the allocation by priority function, but it only works when there is one thing provided and many buyers, and I need to offer several products at the same time.

I have read that Vensim is preparing a multiple allocation function, is it true?
Incase there is no solution in Vensim, does anyone know a proper algorthm for this problem?
Thanks in advance

Marga

[tomfid]

You want DEMAND AT PRICE, SUPPLY AT PRICE and FIND MARKET PRICE. See the sample model in the Help system. https://www.vensim.com/documentation/fn_allocations.htm

[Marga]

Thanks, tomfid, I have got the file but the help documentation of the function I've been able to find is very poor, a little help with that too?...

[Marga]

I'm afraid these functions based on price are not useful for my problem. I must allocate a demand of three products D1, D2 and D3 by three sources S1, s2 and S3 and sources are limited, so that Si and Dj are lower or equal to a limit.

The price based allocation does not allow these limits.
In fact this is an optimization problem, where the share os Dj that go to Si must be allocated with restrictions, do you know if Vensim has optimization functions of this kind?
thanks

Marga

[tomfid]

Enforcing limits on the allocation is exactly what the function does. The price is really just a priority for the allocation process within those constraints.

The solution to the alloc function is optimal if you interpret the priority distribution for each supplier/demander as a cost or utility function, and you can live with the assumption that there are no transportation costs or other unique valuations by demander i for supplier j.

[tomfid]

There's a chapter on the allocation function assumptions and constraints here:
https://www.vensim.com/documentation/al ... erview.htm

It might be possible to do something more complex using FIND ZERO if needed.

It's also possible to do allocation using the optimizer, though not very practical if there are many items and time steps.