Solver Not Respecting Constraints

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Larry Curcio - 25 Dec 2005 14:47 GMT

Is there a known bug where the solver, in nonlinear mode,
ignores constraints? I'm constraining a decision variable to
be positive and getting a negative answer.

Here is a recording of the procedure:

SolverReset
SolverAdd CellRef:="$B$2", Relation:=3, FormulaText:="0.000001"
SolverAdd CellRef:="$C$2", Relation:=3, FormulaText:="0.000001"
SolverAdd CellRef:="$D$2", Relation:=3, FormulaText:="0.000001"
SolverAdd CellRef:="$E$2", Relation:=3, FormulaText:="0.000001"
SolverOk SetCell:="$A$2", MaxMinVal:=1, ValueOf:="0",
ByChange:="$B$2:$E$2"
SolverSolve

The D2 is coming up negative.

Thanks and Regards,
-Larry (New to Excel) Curcio

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kcc - 29 Dec 2005 21:45 GMT

I've run problems with 40 constraints with no problems.
On a problem like this it's easier to enter all the constraints
on one line. e.g.
SolverAdd CellRef:="$B$2:$E$2", Relation:=3, FormulaText:="0.000001"
or in solver by entering the range in the cell reference box.
This is one of those areas where Excel is smart enough to
apply the constraint to each cell in the range and it seems to
do it more consistently than separate constraints.

Also, some option settings can also cause problems,
e.g. high tolerance or low iterations. It may be assuming
a small negative number is close enough for what you are doing
kcc

> Is there a known bug where the solver, in nonlinear mode,
> ignores constraints? I'm constraining a decision variable to
[quoted text clipped - 15 lines]
> Thanks and Regards,
> -Larry (New to Excel) Curcio

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