Why do I get an error message when I try to use the functions QUAD and QUADL?

I receive one of the following messages when I try to pass my inline function or function handle to the QUAD function:

 ??? Error using ==> .*

 Matrix dimensions must agree.

 ??? Error using ==> *

 Inner matrix dimensions must agree.

 ??? Error using ==> *

 Inner matrix dimensions must agree.

 ???Error using ==> ^

 Matrix must be square

Why do I receive these errors and how do I correct the problem?

Answer 1

[MathWorks Support Team]

These errors occur because the function that you are trying to integrate, the integrand, is not defined correctly for use with QUAD and QUADL. You need to write the function in such a way that QUAD/QUADL can accept a vector of values for the dependent variable. This means that the output of F, the function you are integrating, should be the same size as the inputs. Your function F should work as follows with a vector of any size:

 f([a b]) = [f(a) f(b)]   %where a and b are scalar values

 f([a;b]) = [f(a);f(b)]   %where a and b are scalar values

So if you wanted to integrate the function y=x^3, you would need to write it like this:

y = @(x) x.^3;

q = quad(y,0,1);

rather than like this:

y = @(x) x^3;

q = quad(y,0,1);

If you are using a version of MATLAB older than MATLAB 7.0 (R14), you will need to use a function file or an inline function to define the integrand. To perform this integration using an inline function, try:

y=inline('x.^3');

q=quad(y,0,1);

rather than:

y=inline('x^3');

q=quad(y,0,1);