A double integration of the tabulated data.

A double integration of the tabulated data.

Description

A double integration of the tabulated data. f(x,y) may be generated in terms of meshgrid. Double integral computes simply by approximation of the integral for f(x,y) via the trapezoidal method.
Firstly, an integration loop within inner integral over X is performed obtaining the function of area A(y). Secondly, outer loop integration is performed for A(y) over y limits
 Example:
 Q = dblquad(inline('y*sin(x)+x*cos(y)'), pi, 2*pi, 0, pi);
 Q = -9.8696
 [X,Y] = meshgrid(pi:pi/100:2*pi, 0:pi/100:pi );
 Z=Y.*sin(X)+X.*cos(Y);
 int_2D_tabulated(X,Y, Z )
 ans = -9.8688

• MATLAB release: MATLAB 6.5 (R13)
• Other requirements: ---

[dave martin]

If you want to see this code without downloading it, here you go:

function V = int_2D_tabulated(X, Y, Z )
V = trapz( Y(:,1), (trapz(X(1,:),Z, 2)) );

[dave martin]

Sorry, there is no need for the return statement. This is essentially a one liner with a name that is harder to remember than 'trapz' in the first place. This is cumbersome!

[John D'Errico]

But I can call trapz twice with no more effort. Why bother with a special function for something this trivial, since all it does is call trapz twice anyway?