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If you'd like to learn more about designing and solving optimization models for practical business problems, one of your best resources is a textbook aimed at current MBA students.  Visit our Recommended Books page for brief reviews and links to purchase your choice of books. 

If you're using the Solver that comes with Microsoft Excel, you're welcome to visit our Standard Excel Solver support pages.  You'll probably find the answers you need here.  If you're really stuck, contact us and we'll try to help (but our customers with Annual Support Contracts receive priority).

If you're evaluating our Premium Solver or Solver DLL products, we'll give your access to our Excel Product Support and DLL Product Support pages, plus technical support by phone and email at no charge for the first 15 days.  Consulting assistance and Annual Support Contracts are highly recommended as the best way to leverage your own time.  For more information, visit our Technical Support, Software Upgrades, and Consulting Overview.

General Excel Solver Questions

Q.  I'm running the Solver in Excel via a macro. But I don't want the "Solver Results" dialog to be displayed. How do I do this?

A.  Pass "True" as the first argument in your call to the SolverSolve function, e.g. SolverSolve True.  To obtain an integer code corresponding to the Solver Results message, use code = SolverSolve(True).

Q.  I'm trying to run the Solver in Excel via a macro. But as soon as my code calls a Solver function, I get the message "Sub or Function not defined". What am I doing wrong?

A.  You need a reference to the Solver add-in in VBA.  First make sure that you've displayed the Solver Parameters dialog at least once in your Excel session.  Then open the Visual Basic Editor (Alt-F11), select Tools References, and check the box next to Solver.

Q.  When I run the Solver, I get the message "Problem is too large too handle."  But the number of variables and constraints in my model is less than the Solver's size limits. What does this mean?

A.  In older versions of the Solver, this means that there is an error in one of the cells on the right hand side of a constraint.  For example, if you have a constraint A1:A10 >= B1:B10, and B4 contains #VALUE, this message can appear.

Q.  I specified that certain variables in my model have to be integers. But when the Solver runs, I see fractional values in the variable cells. Is there something wrong?

A.  This is normal.  The Solver uses the Branch & Bound method to deal with integer variables.  This means that during the optimization, the Solver will indeed use fractional values, but when the optimal solution is found, all integer variables should have integer values.

Q.  Can I have decision variables on multiple worksheets?

A.  No -- but you can (i) place all decision variable cells on the active sheet, and (ii) refer to these cells on other sheets, thereby in effect using multiple sheets.

General Solver DLL Questions

Q.  I'm using the Solver DLL Platform with Visual Basic.  When I try to run an example, I get the message: "Frontmip.dll not found". What's wrong?

A.  Microsoft Windows looks for DLLs in certain directories -- the current directory, the Windows System directory, and so on.  Visual Basic sets the current directory to its own program directory.  It's easiest to just copy Frontmip.dll to your directory C:\Windows\System or C:\Winnt\System32.

Q.  Whenever I make a call to the Solver DLL Platform routines loadlp() or loadnlp(), they return 0. How can I find out what I'm doing wrong?

A.  Before calling loadlp() or loadnlp(), call the function: setintparam 0, PARAM_ARGCK, 1.  This will cause the Solver DLL to display a message box detailing the nature of the problem.

Q.  OK, I now get a message box when I call loadlp() or loadnlp() -- it says that one of my arguments is "not a valid OLE array." What is that?

A.  If you're using Visual Basic, this probably means you are passing an array name (without subscripts) as an argument and you haven't first called:  setintparam 0, PARAM_ARRAY, 1.  Or, the number of elements in your arrays (compared to the numcols, numrows, and nzspace arguments) might be incorrect.

Questions about Product Evaluations

Q.  I've installed a Premium Solver product with a 15-day evaluation license, and the evaluation period is now expired.  How do I get back the standard Excel Solver?

A.  From the Start menu, select Settings Control Panel (or just Control Panel in Windows XP), then select Add/Remove Programs.  Scroll down to the entry for the Premium Solver product you installed, click Change/Remove, and follow the prompts.  You can also re-run the Setup program (PSPSetup.exe, PSSetup.exe, etc.) and select "Uninstall" from the menu.

Q.  I installed an old version of the Premium Solver (V3.5 or earlier), the 15-day evaluation license expired, the product isn't listed in Add/Remove Programs, and I lost my copy of the Setup program (EvalPlus.exe).  Is there anything I can do to get back the standard Excel Solver?

A.  Carefully do this:  Go to the directory (on most PCs) C:\Program Files\Microsoft Office\Office\Library\Solver (use Office10 for Excel XP).  There should be files solver.xlo and solver32.dlo in this directory.  Delete all the other files in this directory.  Then rename solver.xlo to solver.xla, and rename solver32.dlo to solver32.dll.

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