[Help-glpk] Constraints depending on the data section

[Patrick Meyer]

Hi,

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 ?

Thanx for any suggestion,

Patrick