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# Feedback

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The Open Source Optimization Solver for Excel

We welcome your comments on OpenSolver.

Andrew, I love OpenSolver. It has helped to solve several problems in last years. Thank you and your team for creating and maintaining this great tool!

Thanks for the kind words; I appreciate you taking the time to contact us. I will let the team know. Andrew

Hi

I am running a model but some of my constraints are not being respected.

I am running it on google sheets.

Can someone advise please?

I keep running the model i have entered and nothing happens. it just gives me the spinning wheel of death. I uninstalled the add on, re-installed it, i closed and re-opened sheets, i narrowed my variable cells and parameters, and still nothing happens. every time i try to reset the model, a popup asks me if i really want to reset it, but there is no “okay” or “yes” button, just an “x” to close the popup.

Sorry to hear of your hassles. Is this Windows or Mac Excel or Google Sheets?

OpenSolver for Google Sheets has completely stopped working for me as of one or two months ago.

Is there any way I can contribute to fixing the problem?

Hi. When I run OpenSolver, my constraints are not maintained in the manner in which I set them up. Wondering if anyone would be willing to look at my spreadsheet. When I run the same problem in regular Solver, I have no issues. (The reason I’m using OpenSolver is due to the extra variables, but the overall framework of my problem has not changed.)

Can you explain what is changing? Is it the order of constraints?

When I run the model in regular Solver, my constraints are maintained. However, when I replicate that setup in OpenSolver, the constraints aren’t maintained.

For instance, I’m calculating offensive and defensive ratings for football teams, and the constraints are that the average of all offensive ratings must equal the average number of points scored in each game (and the same thing for defense).

When I run the model, however, even if the average is 23.1 points allowed, each team’s rating goes to zero and thus the average rating goes to zero. And as a result, 0 does not equal 23.1, so the “must equal” constraint is simply not maintained.

Your model almost certainly has a non-linearity in it. Andrew

Dear Andrew Mason

I have written a paper that contains the development of a mathematical model which is then solved by opensolver. After the paper was submitted to an international journal, I received several comments related to the use of opensolver. Among them is about the quality of the solutions produced by OpenSolver. Can the resulting solution be guaranteed to be globally optimal? What kind of algorithm (heuristic method) does opensolver use? Can you help me to answer it?

Thank you

I am pleased you found OpenSolver useful. The solution quality depends on what solver you used. If CBC, then I suggest you read up on Branch and Bound (assuming you have integer variables). If you have no integer variables, then Googling Simplex Algorithm will help you. Hope this helps, Andrew

How to use the latest version of cba, now the version of cbc is long. cba.exe is version 2.9.4. But https://github.com/coin-or/Cbc The cbc version here is already 2.10.7. How to use the new version 2.10.7?

You can simply replace your cbc.exe file with the latest one from the COIN-OR repository https://projects.coin-or.org/Cbc Note that OpenSolver has different CBC versions in ‘Solvers/win32’ and ‘Solvers/win64’, with the solver being chosen to match the 32 or 64 bit status of your operating system. Use the OpenSolver/About OpenSolver menu to see if you are running 32 or 64 bit; eg

“Version 2.9.3 (2020.03.01) running on 64-bit Windows 10.0 with VBA7 in 32-bit Excel 16.0”.

In this case, we are using the 64-bit solver in “Solver/win64”, so this is the one you should replace. You can also see this info under:

CBC v2.9.4 (64-bit) at “D:\Documents\Projects\OpenSolver\OpenSolver2.9.3_Beta_AdvancedWin\Solvers\win64\cbc.exe”

Cheers,

Andrew