Excel solver won't work when a constraint is unsatisfied in the beginning

Question

I have this:

A B C
2 3 A1+B1
4 5 A2+B2

constraint_1: A1 + A2 = 5
constraint_2: B1 + B2 <= 4

Objective cell: C3, which is sum(C1,C2), it should be 0.

When I start with the state above, A1+A2 = 6, solver won't work because constraint_1 is broken in the first place (A1+A2=6). Is there a workaround for this?

Answer 1

Try unchecking the "Make Unconstrained Variables Non-Negative" box in the Solver Parameters Dialog. When I do this, I get a feasible solution of A1=5, B1=0, A2=0, B2=-5.

The nature of your problem is such that there is no feasible solution unless some of the variables are allowed to be negative.

Answer 2

The constraint values need to be put in in the correct order in the solver, for example A1 = B1 might not work, but B1 = A1 will. It depends which is a fixed value and which is the calculated value.

The calculated value should be on the left. If you place the fixed value on the left it simply wont work.