Re: [Help-glpk] [Fwd: Constraints on 2 successive elements of a set]

[Andrew Makhorin]

-------- Forwarded Message --------
From: paterijk <address@hidden>
To: address@hidden
Subject: Re: [Help-glpk] [Fwd: Constraints on 2 successive elements of a
set]
Date: Tue, 20 Nov 2012 11:27:10 -0800 (PST)

Sure, that works. Didn't know about these conditions that one can add in the
definition of a set. Great!

However this does not work with a set containing some strings ... imagine
that instead of "J := 1 2 3;" I would define "J := one two three;" in the
data part to make the output more comprehensible. 

Thanks anyway for this solution, 

Patrick


Meketon, Marc-2 wrote:
> 
> Would this work for you?
> 
> 
> 
> set J;
> 
> var x{i in J};
> 
> 
> 
> s.t. c{i in K : i < card(J)} x[i] >= x[i+1]
> 
> 
> 
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On Behalf
> Of Andrew Makhorin
> Sent: Tuesday, November 20, 2012 1:15 PM
> To: address@hidden
> Subject: [Help-glpk] [Fwd: Constraints on 2 successive elements of a set]
> 
> 
> 
> -------- Forwarded Message --------
> 
> From: paterijk <address@hidden<mailto:address@hidden>>
> 
> To: address@hidden<mailto:address@hidden>
> 
> Subject: [Help-glpk] Constraints on 2 successive elements of a set
> 
> Date: Tue, 20 Nov 2012 09:40:00 -0800 (PST)
> 
> 
> 
> Hi,
> 
> 
> 
> I'm trying to model a constraint using the GMPL modeling language.
> 
> 
> 
> To start, we have a set of n indices called J, and a variable vector x
> with n components. The constraint then should look like :
> 
> 
> 
> x_i >= x_{i+1} for i=1..n-1 (obviously we do not want i+1 to go beyond the
> limits of J)
> 
> 
> 
> What I do is the following, but I do not find it very elegant :
> 
> 
> 
> set J;
> 
> set K;
> 
> var x{i in J};
> 
> 
> 
> s.t. c{i in K} x[i] >= x[i+1]
> 
> 
> 
> In the data section I then define :
> 
> 
> 
> set J := 1 2 3;
> 
> set K := 1 2;
> 
> 
> 
> Does anybody know how to handle this without having to go through this set
> K which I have to adapt in the data section when the set J changes? K is
> just J minus the last element. Note that this also does not work when J
> (and K) contain non numerical elements (because of the i+1 in the
> constraints).
> 
> 
> 
> Thanks for any hint,
> 
> 
> 
> Patrick
> 
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> 
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