Rookie Needs help regarding Binary Variables in Solver

[hogo1502]

Hi

I would appreciate if anybody could answer this small question: In Solver, If a I have a cell whose value is set to be binary, + the cell is also a changing cell, Do I need to set the value equal to 1, before running the Solver?

Example:

Set C3 = 0 <--- this is my x variable, set to be Integer, and a Changing Cell in Solver
Set C4 = 0 <--- this is my y variable, set to be Binary, and a Changing Cell

Constraint: C6=2*x*y <= 11

Target Cell: Maximizing C8: = C3*C4

Why is it that if C4=0 before running the Solver it gives me 0's in all cells after running it, but if C4=1 it actually does succeed to solve the problem (giving me x=5)? Surely when C4 is set as Changing Cell it should still find the solution!!

 

[shg]

Trivially, C4 must be something other than 0 to maximize C8. Why set it as a changing cell at all?

In my experience, Solver works best with smooth functions, where it can get its whole partial derivative thing going. Evaluation of multiple functions (induced by binary constraints), evaluations involving enumerated values (induced by integer constraints) and flat spots (induced by rounding anywhere in the calculation chain) make its life more difficult.

 

[hogo1502]

This is just a very simplified version of a bigger problem. I have an inventory management problem where at every quarter of the year I need to decide whether I am going to order a particular item or not. I have modelled this decision variable as a binary variable y. The problem is that

1. if I initialize these variables to 0, then run the Solver, it immediately says "Solver could not find a feasible solution."
2. If I set them to 1, Solver gives a solution (but not the one I want. I know the correct solution already).

Normally the best case would be able to leave these blank and let the Solver do its magic but when I do that, it returns "Solver could not find a feasible solution."

That's why I came with this simple example. Don't understand why the Solver can't even find the wrong answer when y cell is set to 0 or left blank.