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Limits on Constraints
If you have a linear problem -- and you've checked
the Assume Linear Model box in the Solver Options dialog -- there is
no limit on the number of constraints. If you have not checked
the Assume Linear Model box, the Solver assumes that the problem
is nonlinear and imposes a limit.
For nonlinear problems, you can place constraints
on up to 100 cells which are not decision variables. In addition,
you can place constant upper and/or lower bounds on the decision
variables, and you can place integer constraints on some or all of
the decision variables.
If you have reached the limit of 100 constraints,
consider these steps:
 | Is the model necessarily nonlinear? If you can
formulate it as a linear model, the constraint limit won't
apply. You may be able to use a piecewise linear
approximation to a nonlinear function. |
| Do you have constraint cells containing simple
formulas like =A1 where A1 is a decision variable? Such cells
count against the limit of 100; but if you apply the constraint
directly to the decision variable cells (and use a constant
right hand side), it won't. |
| Do you have constraints involving (say) just
two decision variables? If so, you might be able to place
individual limits on the variables; this may change the range of
possible solutions, but still allow you to make some progress. |
| Do you have constraints where the right hand
side is a cell or cells whose value depends on the decision
variables? The Solver treats constraints like A1 <= A2 as if
they were written A1-A2 <= 0, and counts them against the
constraint limit -- even if A1 is a decision variable. Try to
replace these constraints with individual cell limits if
possible. |
| Do you have constraints where the right hand
side (RHS) is a formula, rather than a constant or a reference
to cells which are constant? The Solver treats all RHS formulas
as variable -- so A1 <= 2+2 would count against the
constraint limit, even if A1 is a decision variable. |
You may find that upgrading to Frontline's Premium
Solver products is a more efficient use of your time. The Premium
Solver has a limit of 8192 constraints for linear problems, and 250 constraints for nonlinear problems
(apart from bounds on the variables and integer constraints) -- and
it solves problems of this size in much less time. Our Large-Scale GRG Solver handles problems with thousands of constraints, in
addition to bounds on the variables.
Back to Standard Excel Solver
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