Microsoft Office Tutorials and References

In Depth Information

**TROUBLESHOOTING SOLVER**

TROUBLESHOOTING SOLVER

Solver is a fairly complex software program. This section helps you address common problems you may

encounter when attempting to run Solver.

Using Whole Numbers in Changing Cells

Before you run your first Solver model or rerun a previous model, always enter a positive whole number in

each of the Changing Cells. If you have not already defined maximum and minimum constraints for the

values in the Changing Cells, enter 1 in each cell before running Solver.

Getting Negative or Fractional Answers

If you receive negative or fractional answers when running Solver, you may have neglected to specify one or

more of the Changing Cells as non-negative integers. Alternatively, if you are working on a cost minimization

problem and you fail to specify the Optimization Cell as non-negative, you may receive a negative answer for

the cost. Sometimes Solver will also warn you that you have one or more unbounded constraints (see

Figure D-49).

FIGURE D-49

Solver has an “unbounded” objective function because you did not specify non-negative integer

constraints

Creating Overconstrained Models

If Solver cannot find a solution because it cannot meet the constraints you defined, you will receive an error

message. When this happens, Solver may even violate the integer constraints you defined in an attempt to

find an answer, as shown in Figure D-50.