Asking Excel Solver to use binaries, but selects other values

[Guest]

I am trying to get a linear program solved using solver. The values that
Solver needs to enter are contrained as binary, but excel still try to find
values that are neither 0 or 1.

 

[Guest]

Stephane,

I assume that when you say it is selecting values that are neither 0 or 1,
they are values that are numerically close to 0 or 1 (such as 0.99998). If
this is the case, you may want to consider the following approach:

1. Have the Solver constrain your decision variables as binary.
2. Have another set of cells which uses the decision variable to produce a
result. When the underlying decision variable is close enough to a 0 or 1,
have it return exactly a 0 or 1 (and not the numerical approximation
generated by the Solver).
3. Use this underlying result instead of the underlying decision variable in
your objective function.

 

[Guest]

Actually, Solver is trying values such as 0.52, 0.17, and so on. I will try
to use other cells and convert back the values to 0 or 1.

Thanks for the quick answer,

Stephane

 

[Tushar Mehta]

No, please don't second guess Solver. It won't help Solver find a
solution and you will likely land up at a wrong result.

Solver uses a well-established technique called branch and bound. This
technique 'relaxes' the integer/binary constraints and then
reestablishes them towards the end of the analysis.

If Solver shows you a non-binary result it probably also pops up an
alert of one kind or another -- maybe, about how it cannot find a
solution?

Have you specified your problem as 'linear?' In the Solver dialog box
click the Options button. Those kinds of problems are the most easily
solved by the techniques programmed into Solver. Of course, it is up
to you to ensure that the requirements of linearity (as defined in
Operations Research) are met.


--
Regards,

Tushar Mehta
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
Custom MS Office productivity solutions