MATLAB

The Language of Technical Computing

Function Functions

This example shows how to use the output of one MATLAB® function as an input to another. This ability to specify a function's output as an input of another function serves a wide variety of purposes. Here we illustrate its use for finding zeros, optimization, and integration.

The HUMPS Function

A MATLAB function is a file that starts with the keyword function. This is what the function HUMPS looks like:

type humps
function [out1,out2] = humps(x)
%HUMPS  A function used by QUADDEMO, ZERODEMO and FPLOTDEMO.
%   Y = HUMPS(X) is a function with strong maxima near x = .3
%   and x = .9.
%
%   [X,Y] = HUMPS(X) also returns X.  With no input arguments,
%   HUMPS uses X = 0:.05:1.
%
%   Example:
%      plot(humps)
%
%   See QUADDEMO, ZERODEMO and FPLOTDEMO.

%   Copyright 1984-2014 The MathWorks, Inc.

if nargin==0
   x = 0:.05:1;
end

y = 1 ./ ((x-.3).^2 + .01) + 1 ./ ((x-.9).^2 + .04) - 6;

if nargout==2,
   out1 = x;
   out2 = y;
else
   out1 = y;
end

Plot of HUMPS

This figure shows a plot of HUMPS in the domain [0,2] using FPLOT.

fplot(@humps,[0,2]);

Zero of HUMPS

The FZERO function finds a zero of a function near an initial estimate. Our initial guess for the zero of HUMPS is 1.

z = fzero(@humps,1,optimset('Display','off'));
fplot(@humps,[0,2]);
hold on;
plot(z,0,'r*');
hold off

Minimum of HUMPS

The FMINBND function finds the minimum of a function in a given domain. Here, we search for a minimum for HUMPS in the domain (0.25, 1).

m = fminbnd(@humps,0.25,1,optimset('Display','off'));
fplot(@humps,[0 2]);
hold on;
plot(m,humps(m),'r*');
hold off

Integral of HUMPS

The INTERGRAL function finds the definite integral of HUMPS in a given domain. Here it computes the area in the domain [0.5, 1].

q = integral(@humps,0.5,1);
fplot(@humps,[0,2]);
title(['Area = ',num2str(q)]);