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Solver Iterations-how to change number (Microsoft Excel Question)


Fri, 23 May 2008 00:45:00 GMT, 3 comments.

Hi,

When I try to change the number of solver iterations I can't seem to

actually get it to do more than about 5. I walked through the iterations

step-by-step and after about 5 iterations it quits. If I start from that

solution a couple more times it gets to the solution, so I seem to have a

simple problem that only requires about 15 iterations but changing the number

of iterations allowed doesn't seem to have an effect. I have tried

everything that seems obvious.

Thanks.


tags: excel, iterations, iterations-how, microsoft, msdn, number, software, solver, walked


  1. In Help, under "Troubleshoot Solver," there are a number of reasons

    why Solver might stop prematurely. For instance, "For problems with

    integer constraints, you need to decrease the Tolerance setting in the

    Solver Options dialog box so that Solver can find a better integer

    solution."

    If that example isn't the problem, you might want to peruse the

    others.

    Mark Lincoln

    On Sep 27, 3:04 pm, Rick Hicks <Rick Hi....excel.todaysummary.com.discussions.microsoft.com>

    wrote:

    > Hi,

    > When I try to change the number of solver iterations I can't seem to

    > actually get it to do more than about 5. I walked through the iterations

    > step-by-step and after about 5 iterations it quits. If I start from that

    > solution a couple more times it gets to the solution, so I seem to have a

    > simple problem that only requires about 15 iterations but changing the number

    > of iterations allowed doesn't seem to have an effect. I have tried

    > everything that seems obvious.

    > Thanks.

  2. If it quits, then Solver cannot improve the solution or it converges on a

    value. Have you played with all the options in Solver? Have you decreased

    the convergence?

    Otherwise, perhaps you really are at the optimal value. I've found that

    when setup correctly, Solver is pretty darn accurate. With all due respect

    to PivotTables, I believe Solver is the most powerful and useful tool (at

    least to us engineers).

    Matthew Pfluger

    "Rick Hicks" wrote:

    > Hi,

    > When I try to change the number of solver iterations I can't seem to

    > actually get it to do more than about 5. I walked through the iterations

    > step-by-step and after about 5 iterations it quits. If I start from that

    > solution a couple more times it gets to the solution, so I seem to have a

    > simple problem that only requires about 15 iterations but changing the number

    > of iterations allowed doesn't seem to have an effect. I have tried

    > everything that seems obvious.

    > Thanks.

  3. Thanks,

    I found the problem in the troubleshooting. I didn't know if it was

    something I would find there or if it was a trick that one of you experts

    would know (the first time I trolled this site the result to my problem was a

    clever little wrinkle). It turns out I got tired of looking right before I

    got to it.

    For anyone else stumbling onto this thread in the future, the problem I was

    seeing was a "...could not find a feasible solution" message after a few

    iterations. The solver would eventually work if I redid it a few times,

    restarting with the previous run's results for my variables.

    The solution was to check the "Use automatic scaling" box. I have a problem

    where my variables range from 1 mil to 10 mil and when I start with all of

    them at zero the range is too wide for the solver to deal with.

    Thanks again for the help. Know there wasn't a special "trick" helped a lot.

    Rick

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