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

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: help-glpk-bounces+address@hidden [mailto:help-glpk-bounces+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>

To: 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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From:	Meketon, Marc
Subject:	Re: [Help-glpk] [Fwd: Constraints on 2 successive elements of a set]
Date:	Tue, 20 Nov 2012 12:25:48 -0600