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Denise Sakai Troxell (2000) Handling Some of the Problems Encountered When Using Excel Solver for Microsoft Excel 2000

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Denise Sakai Troxell (2000) Some Common Sources of Problems it is possible that the… time or iteration limit was reached; precision is too large ; convergence to the solution is too slow; model is poorly scaled; choice of initial solution is inadequate; solution was affected by limitations on finite precision computer arithmetic; solution is right and your expectation is wrong…

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Denise Sakai Troxell (2000) Modifying Solver Options Recall: Solver Options dialog box with default values

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Denise Sakai Troxell (2000) Modifying Solver Options if time or iteration limit was reached NOTE: The message in the Solver Results dialog box will indicate that either the time or iteration limits were reached. Increase the value in the Max Time: box and/or Iterations: box

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Denise Sakai Troxell (2000) Modifying Solver Options if the precision is too large NOTE: Constraints are checked within the precision specified in the Precision: box (smaller value means higher precision). Decrease the value in the Precision: box

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Denise Sakai Troxell (2000) Modifying Solver Options if the convergence is too slow NOTE: The message in the Solver Results dialog box will indicate that Solver converged to the current solution. This means that the last five iterations showed relative changes smaller than the value in the Convergence: box. Decrease the value in the Convergence: box

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Denise Sakai Troxell (2000) Modifying Solver Options if the model is poorly scaled Check the Use Automatic Scaling: box to rescale values to a common magnitude NOTE: A model is poorly scaled if it deals with values which have large differences in magnitude. This is the most common source of problems when using Solver. NOTE: A model is poorly scaled if it deals with values which have large differences in magnitude. This is the most common source of problems when using Solver.

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Denise Sakai Troxell (2000) Modifying Solver Options other Options For more about other Options, click on Help WARNING: Additional mathematical background might be required to understand some of the remaining options.

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Denise Sakai Troxell (2000) Selecting Initial Values if the initial values are inadequate NOTE: In optimization problems Solver usually finds a local optimum solution that is close to the initial variable values. Run Solver with initial variable values (on the spreadsheet) that may be closer to the global optimum solution. Recall: Variable values in the cells shown in the By Changing Cells: box of the Solver Parameters dialog box

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Denise Sakai Troxell (2000) Finite Precision Computer Arithmetic not Solver’s fault… Computers store numbers in binary format (as sequences of 0’s and 1’s); Some numbers in binary format cannot be represented in a finite amount of space and need to be rounded when stored; If several arithmetic operations are performed on the rounded representations, rounding errors may accumulate.

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