Solver Options

You can control advanced features of the solution process, load or save problem definitions, and define parameters for both linear and nonlinear problems. Each option has a default setting that is appropriate for most problems.

Max time     Limits the time taken by the solution process. While you can enter a value as high as 32,767, the default value of 100 (seconds) is adequate for most small problems.

Iterations     Limits the time taken by the solution process by limiting the number of interim calculations. While you can enter a value as high as 32,767, the default value of 100 is adequate for most small problems.

Precision     Controls the precision of solutions by using the number that you enter to determine whether the value of a constraint cell meets a target or satisfies a lower or upper bound. Precision must be indicated by a fractional number between 0 (zero) and 1. Higher precision is indicated when the number that you enter has more decimal places — for example, 0.0001 is higher precision than 0.01.

Tolerance     The percentage by which the target cell of a solution satisfying the integer constraints can differ from the true optimal value and still be considered acceptable. This option applies only to problems with integer constraints. A higher tolerance tends to speed up the solution process.

Convergence     When the relative change in the target cell value is less than the number in the Convergence box for the last five iterations, Solver stops. Convergence applies only to nonlinear problems and must be indicated by a fractional number between 0 (zero) and 1. A smaller convergence is indicated when the number that you enter has more decimal places — for example, 0.0001 is less relative change than 0.01. The smaller the convergence value, the more time Solver takes to reach a solution.

Assume Linear Model     Select to speed the solution process when all relationships in the model are linear and you want to solve a linear optimization problem.

Assume Non-Negative     Causes Solver to assume a lower limit of 0 (zero) for all adjustable cells for which you have not set a lower limit in the Constraint box in the Add Constraint dialog box.

Use Automatic Scaling     Select to use automatic scaling when inputs and outputs have large differences in magnitude — for example, when maximizing the percentage of profit based on million-dollar investments.

Show Iteration Results     Select to have Solver pause to show the results of each iteration.

Estimates

Specifies the approach that is used to obtain initial estimates of the basic variables in each one-dimensional search.

Tangent     Uses linear extrapolation from a tangent vector.

Quadratic     Uses quadratic extrapolation, which can improve the results on highly nonlinear problems.

Derivatives

Specifies the differencing that is used to estimate partial derivatives of the objective and constraint functions.

Forward     Use for most problems, in which the constraint values change relatively slowly.

Central     Use for problems in which the constraints change rapidly, especially near the limits. Although this option requires more calculations, it might help when Solver returns a message that it could not improve the solution.

Search

Specifies the algorithm that is used at each iteration to determine the direction to search.

Newton     Uses a quasi-Newton method that typically requires more memory but fewer iterations than the Conjugate gradient method.

Conjugate     Requires less memory than the Newton method but typically needs more iterations to reach a particular level of accuracy. Use this option when you have a large problem and memory usage is a concern, or when stepping through iterations reveals slow progress.

Load Model     Displays the Load Model dialog box, where you can specify the reference for the model that you want to load.

Save Model     Displays the Save Model dialog box, where you can specify where to save the model. Click only when you want to save more than one model with a worksheet — the first model is automatically saved.