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Optimization Solver Plot Functions

What Is a Plot Function?

The PlotFcns field of the options structure specifies one or more functions that an optimization function calls at each iteration to plot various measures of progress. Pass a function handle or cell array of function handles. The structure of a plot function is the same as the structure of an output function. For more information on this structure, see Optimization Solver Output Functions.

You can use the PlotFcns option with the following MATLAB® optimization functions:

The predefined plot functions for these optimization functions are:

  • @optimplotx plots the current point

  • @optimplotfval plots the function value

  • @optimplotfunccount plots the function count (not available for fzero)

To view or modify a predefined plot function, open the function file in the MATLAB Editor. For example, to view the function file for plotting the current point, enter:

edit optimplotx.m

Example: Plot Function

View the progress of a minimization using fminsearch with the plot function @optimplotfval:

  1. Write a file for the objective function. For this example, use:

    function f = onehump(x)

r = x(1)^2 + x(2)^2;
s = exp(-r);
f = x(1)*s+r/20;

  2. Set the options to use the plot function:

    options = optimset('PlotFcns',@optimplotfval);

  3. Call fminsearch starting from [2,1]:

    [x ffinal] = fminsearch(@onehump,[2,1],options)

  4. MATLAB returns the following:

    x =
   -0.6691    0.0000

ffinal =
   -0.4052

    As the iterations proceed, the function value first decreases, then becomes constant.

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