D.4.2 glpk output

If a solution meeting the constraints is found, it is returned as a list of pairs of the form <(i,x)...>, where each i is a natural number and each x is a floating point number giving the value obtained for the i-th variable numbered from zero. Any values of i that are omitted from the list indicate that the corresponding variable has a value of zero.

If no solution is found due to infeasibility or because glpk just didn't find one, an empty list is returned. The lack of a solution is not treated as an exceptional condition.