# Basic Solver - Change Options for GRG Nonlinear Solving Method

1. In the Solver Parameters dialog box, click Options.
2. In the Solver Options dialog box, on the GRG Nonlinear tab, choose one or more of the following options:

Convergence

• In the Convergence box, type the amount of relative change that you want to allow in the last five iterations before Solver stops with the message “Solver converged to the current solution.” Smaller values here usually mean that Solver will take more time, but will stop at a point closer to the optimal solution.

Derivatives

• In the Derivatives group box, select Forward to estimate derivatives through forward differencing, or select Central to estimate derivatives through central differencing. Forward is the default choice. Central differencing yields more accurate derivatives, but requires twice as many calculations of the worksheet at each new trial solution.

MultiStart Options for Global Optimization

• Select the Use Multistart check box to use the multistart method for global optimization. If this box is selected when you click Solve, the GRG Nonlinear method will be run repeatedly, starting from different (automatically chosen) starting values for the decision variables. This process may find a better solution, but it will take more computing time than a single run of the GRG Nonlinear method.
• In the Population Size box, type the number of different starting points (values for the decision variables) you want the multistart method to consider. The minimum population size is 10; if you supply a value less than 10 in this box, or leave it blank, the multistart method uses a population size of 10 times the number of decision variables, but no more than 200.
• In the Random Seed box, type a positive integer number to be used as the (fixed) seed for the random number generator used to generate candidate starting points for the GRG Nonlinear method. If you enter a number here, the multistart method will use the same starting points each time you click Solve. If you leave this box blank, the random number generator will use a different seed each time you click Solve, which may yield a different (better or worse) final solution.
• Select the Require Bounds on Variables check box to specify that the multistart method should run only if you have defined lower and upper bounds on all decision variables in the Constraints list box. The multistart method is far more effective if you define bounds on all variables; the tighter the bounds on the variables that you can specify, the better the multistart method is likely to perform.

NOTE   You can click the Help button in the dialog box to get more information about other options.