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Re: [Help-glpk] forall and exists?
From: |
xypron . glpk |
Subject: |
Re: [Help-glpk] forall and exists? |
Date: |
Tue, 7 May 2013 12:54:10 +0200 (CEST) |
Hello Andrew,
GLPK is a linear programming solver. A constraint with an IF would not be
linear.
In linear programming you might introduce binary variables for your purpose.
Or use a constraint programming solver.
Best regards
Heinrich Schuchardt
http://www.xypron.de
Am 07.05.13 um 07:48 schrieb Jay Hutfles
> Oh, I don't think there's anything wrong with them. Well, except for how
>
> I'm trying to use them.
>
>
>
> I see that the examples only use them in computable parameters, though. I
>
> was trying to use them in constraints, and was getting errors along the
>
> lines of "forall function does not exist" (sorry, I don't have the exact
>
> error with me). The constraints were of the form:
>
>
>
> for all a in A, if x[a] =1 then there exists a b in B such that
>
> (something or another based on a)
>
>
>
> I was having trouble directly implementing constraints of this form, so I
>
> changed the "if p then q" form to "not p or q" like this:
>
>
>
> subject to C {a in A} :
>
> (1 - x[a]) + (if exists {b in B} (...something or other based on a..)
>
> then 1 else 0) >= 1;
>
>
>
> I'll have to try again in the morning when I'm more awake. Thanks for the
>
> guidance, Andrew.
>
>
>
>
>
>
>
> On Mon, May 6, 2013 at 11:36 PM, Andrew Makhorin <address@hidden> wrote:
>
>
>
> >
>
> > > Can you provide a link to an example of each? Any help would be
>
> > > appreciated.
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> > >
>
> >
>
> > Please see glpk/examples/color.mod (for 'exists') and
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> > glpk/examples/egypt.mod (for 'forall').
>
> >
>
> > What is wrong with these operators?
>
> >
>
> >
>
> >
>
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>
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>
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>
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