Re: [Help-glpk] Constraints depending on the data section

[Andrew Makhorin]

> Part of my problem looks as follows:

> set X;
> var stilde{j in X, k in X} >=-1, <=1;

> where the variable stilde is constrained by a few conditions in the 
> problem.

> Depending on the data section, I want to add some more constraints, 
> which I don't know how to express.

> Imagine that in the data section I have:

> set X := a b c d;

> I would now like to express somehow in a constraint that

stilde[a,b] >= delta;
stilde[a,c] >= delta;

> where delta is a parameter. Note that depending on the problem, these
> constraints could involve different pairs of elements of X. That is why
> they have to be defined in the data section.

> I thought that I could add a parameter

> param stildeConstraint : 1 2 :=
> 1 a b
> 2 a c ;

> in the data section to express this, and write in the constraints section:

> s.t. constOutranking{i in 1..2}: stilde[stildeConstraint[i,1], 
> stildeConstraint[i,2]] >= delta;

> Nevertheless, this does not seem to be appropriate.

> I receive as an error:

> "stildeConstraint requires numeric data"

> Does anybody know how this can be done in a more correct way ?

You should declare stildeConstraint as symbolic, e.g.

param stildeConstraint{...}, symbolic, in X;