Question

I try to draw the Mexican hat function using Matlab.

x=-20:20;
y=-20:20;
z=(1 - x.^2 -y.^2) * exp(-1/2 * (x.^2 + y.^2))

But I got error:

??? Error using ==> mtimes
Inner matrix dimensions must agree.

How should do to I fix it? Thanks

Answer 1

There are two bugs here. First, you want to create your x and y using something like meshgrid, so that they are arrays rather than vectors (and while we’re at it, let’s look at a more edifying range for the function…)

>> [x y] = meshgrid(-5:0.5:5, -5:0.5:5);

Second, you want element-wise multiplication instead of matrix multiplication (.* instead of *).

>> z = (1 - x.^2 -y.^2) .* exp(-1/2 * (x.^2 + y.^2));

That should do the trick:

>> surf(z)