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#1
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Solver does not find correct solution???
Hello,
I have recently had a problem with excel's solver (until last week I never had a porblem). When fitting a data set (trying to minimize my target cell), the solver says that either it has found a solution or that the data doesn't converge. When I run the solver again, my target cell is further reduced or the cells don't converge again. When running my spreadsheet on a colleagues computer, there is no problem, so I know the problem isn't with my data. Any help or suggestions would be greatly appreciated! Thanks in advance. |
#2
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experiment626 -
Check (and perhaps adjust) the settings (precision, tolerance, convergence, etc.) on Tools | Solver | Options. - Mike www.mikemiddleton.com "experiment626" wrote in message ... Hello, I have recently had a problem with excel's solver (until last week I never had a porblem). When fitting a data set (trying to minimize my target cell), the solver says that either it has found a solution or that the data doesn't converge. When I run the solver again, my target cell is further reduced or the cells don't converge again. When running my spreadsheet on a colleagues computer, there is no problem, so I know the problem isn't with my data. Any help or suggestions would be greatly appreciated! Thanks in advance. |
#3
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H Mike, Thanks for your response, but I have already looked at that and I
have not changed any of my settings from when the solver used to work for me with no problems. Any other suggestions? Thanks in advance. |
#4
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For non-linear non-convex problems, Solver, like most other
optimization packages, cannot guarantee a global optimum. It might work depending on the options selected as well as the starting values for a specific solution attempt. As far as not changing any setting from when solver used to work, how could you possibly do that? I used Solver a few times yesterday, and I couldn't tell you what my option settings were! It is hard to imagine someone being in the habit of noting or otherwise memorizing the settings for max.time, max.iterations, precision, tolerance, convergence, estimates, derivaties, search, etc. On your colleague's computer and your own, open the workbook you are having problems with. Compare the values of *all* the cells in the model. Open the solver dialog box, click Options. Note the values of *all* 12 settings. Are there any differences between the two? Now, what happens if you ask Solver to solve the problem? -- Regards, Tushar Mehta www.tushar-mehta.com Excel, PowerPoint, and VBA add-ins, tutorials Custom MS Office productivity solutions In article , says... H Mike, Thanks for your response, but I have already looked at that and I have not changed any of my settings from when the solver used to work for me with no problems. Any other suggestions? Thanks in advance. |
#5
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Hi Tushar Mehta,
Thanks for your response. I have really checked and rechecked the settings many times, nothing has changed. I use the solver many times daily with always the exact same model on different data. The settings are the same EVERY time, they never change. To make things more frusterating, when my collegue logs onto my computer (he has a login account on my computer) he can run the solver without the problem I have when I am logged in. I understand that the solver can not guarantee a golbal optimum, but usually it works for several hours before finding a solution. My problem is that is now quits after about 5 minutes and says that it has found a solution. It is not possible for a solution to be found so quickly with my data. When i run the solver again, it calculates for a few minutes and then quits again, I could do that all day... As i said, I just started having this problem last week. I have tried COMPLETELY uninstalling office, I have tried installing a different office version, always with the same problem. Any other suggestions? Thank you!!!! |
#6
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For non-linear non-convex problems, Solver, like most other
optimization packages, cannot guarantee a global optimum. It might work depending on the options selected as well as the starting values for a specific solution attempt. Tushar, As a side note, the nonlinear nonconvex problems can now reach a proved global optimum, thans to the new technology progress. Of particular approach is the one based on convexification and branch-and-bound methods. This guaranteed approach is also availabe in an Excel addin solver, namely What's Best. If you are interested, you might want to check out the product website at www.lindo.com. As I know, there is a free version with limited capacity. Regards, Tony |
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