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Chapter 16. Solving Complex Problems wit... > Selecting the Method Solver Uses

Selecting the Method Solver Uses

The options in the Estimates, Derivatives, and Search groups at the bottom of the dialog box control the method Solver uses. The default options perform the job in the vast majority of cases. However, here's a quick rundown of the options, in case you need them:

  • Estimates— These two options determine how Solver obtains its initial estimates of the model variables. The Tangent option is the default. You need to select Quadratic only if your model is highly nonlinear.

  • Derivatives— Some models require Solver to calculate partial derivatives. These two options specify the method Solver uses to do this. Forward differencing is the default method. The Central differencing method takes longer than forward differencing, but you might want to try it when Solver reports that it can't improve a solution. (See the section later in this chapter entitled “Making Sense of Solver's Messages.”)

  • Search— When finding a solution, Solver starts with the initial values in the model and then must decide which direction to take to adjust the variables. These options determine the method Solver uses to make this decision. The default Newton option tells Solver to use a quasi-Newton search method. This method uses more memory, but it's faster than the Conjugate method, which uses a conjugate gradient search. Usually, you'll need to select Conjugate only for large models in which memory is at a premium.


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