Assume Non-Negative

When this box is checked, any decision variables without explicit lower bounds (>= constraints) in the Constraints list box of the Solver Parameters dialog will be given a lower bound of zero when the problem is solved. This option has no effect for decision variables which do have explicit >= constraints, even if those constraints allow the variables to assume negative values. For example, a constraint A1 >= -3 specifies that A1 can assume values from -3 to 0, even if the Assume Non-Negative box is checked.