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Re: [Help-glpk] More conditional variables fun

From: Michael Hennebry
Subject: Re: [Help-glpk] More conditional variables fun
Date: Tue, 13 Oct 2009 07:12:31 +0400

This might bounce from the list.
NDSU is mucking with my return address.
Kretchmer wrote:

> Thanks Larry. What I was looking for is for a way of forcing the "C"
> variable to equal values per the truth table.
> If "C" was binary I could achieve this by a series of inequalities without
> big M, and I'm just wondering what would be the formulation for non-binary
> variables.

In my previous post, I seem to have misinterpreted the question.

Unless you have bounds on the differences in the variables,
there isn't any good way.
With bounds on the differences,
the feasible sets of (a,b,c-d) and (a,b,c-e)
have four extreme points.
Their convex hulls are tetrahedra.

>> Now I'd like to be able to model conditional non-binary variables. Does
>> anybody know how to formulate this in mathprog?
>> ----------Begin Description -------------------
>> *) a,b are binary
>> *) c,d,e is continuous.
>> *) I'd like c to be
>>     - 0 if a=b=0
>>     - d if a=0,b=1
>>     - e if a=1,b=0
>>     - 0 if a=b=1
>> ----------End Description

Michael   address@hidden
"Pessimist: The glass is half empty.
Optimist:   The glass is half full.
Engineer:   The glass is twice as big as it needs to be."

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