I'm new at using the glpk tool, and after writing a model for certain integer problem and running the solver (glpsol) i get negative values in some constraint that shouldn't be negative at all:

 No.Row name  Activity     Lower bound   Upper bound
 8 act[1]     0                          -0 
 9 act[2]    -3                          -0 
10 act[2]    -2                          -0 

That constraint is defined like this: act{j in J}: sum{i in I} d[i,j] <= y[j]*m;

where the sets and variables used are like this: param m, integer, > 0;

param n, integer, > 0;

set I := 1..m;

set J := 1..n;

var y{j in J}, binary;

As the upper bound is negative, i think the problem may be in the y[j]*m parte, of the right side of the inequality.. perhaps something with the multiplication of binarys? or that the j in that side of the constrait is undefined? i dont know... i would be greatly grateful if someone can help me with this! :) and excuse for my bad english

thanks in advance!