dblquad (MATLAB Functions)

Numerically evaluate double integral

Syntax

q = dblquad(fun,xmin,xmax,ymin,ymax)
q = dblquad(fun,xmin,xmax,ymin,ymax,tol)
q = dblquad(fun,xmin,xmax,ymin,ymax,tol,method)

Description

q = dblquad(fun,xmin,xmax,ymin,ymax) calls the quad function to evaluate the double integral fun(x,y) over the rectangle xmin <= x <= xmax, ymin <= y <= ymax. fun is a function handle. See Function Handles in the MATLAB Programming documentation for more information. fun(x,y) must accept a vector x and a scalar y and return a vector of values of the integrand.

Parameterizing Functions Called by Function Functions, in the MATLAB mathematics documentation, explains how to provide additional parameters to the function fun, if necessary.

q = dblquad(fun,xmin,xmax,ymin,ymax,tol) uses a tolerance tol instead of the default, which is 1.0e-6.

q = dblquad(fun,xmin,xmax,ymin,ymax,tol,method) uses the quadrature function specified as method, instead of the default quad. Valid values for method are @quadl or the function handle of a user-defined quadrature method that has the same calling sequence as quad and quadl.

Example

Pass M-file function handle @integrnd to dblquad:

```
Q = dblquad(@integrnd,pi,2*pi,0,pi);
```

where the M-file integrnd.m is

function z = integrnd(x, y) 
z = y*sin(x)+x*cos(y);

Pass anonymous function handle F to dblquad:

F = @(x,y)y*sin(x)+x*cos(y);
Q = dblquad(F,pi,2*pi,0,pi);

The integrnd function integrates y*sin(x)+x*cos(y) over the square pi <= x <= 2*pi, 0 <= y <= pi. Note that the integrand can be evaluated with a vector x and a scalar y.

Nonsquare regions can be handled by setting the integrand to zero outside of the region. For example, the volume of a hemisphere is

dblquad(@(x,y)sqrt(max(1-(x.^2+y.^2),0)), -1, 1, -1, 1)

dblquad(@(x,y)sqrt(1-(x.^2+y.^2)).*(x.^2+y.^2<=1), -1, 1, -1, 1)

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