We consider Linear Programming problems (either continuous or integer) where some
matrix entries can be fixed by the decision maker to any value within an
interval. In the assumption of non negativity of the variables the problem can be solved in two phases. First the
variables are computed and then this solution is used to
compute the matrix entries. In the paper it is also shown that introducing direct costs on the
variable matrix entries makes the problem NP-hard. Finally a kind of strong duality result is provided for this problem.
