Matlab Replacing Loop with Range Expression

Question

I have function called buildRay which returns a 1x4 matrix. I call it multiple times like so:

rays = zeros(numRays, 4);
for j = 1:numRays
    rays(j, :) = buildRay(particle, (j-1)*anglePart, rayLength);
end

If I try and replace the loop with:

rays(1:numRays, :) = buildRay(particle, ((1:numRays)-1).*anglePart, rayLength);

I get the following error

??? Subscripted assignment dimension mismatch.

and I don't understand why.

Could someone please tell me what I'm doing wrong?

Thanks.

Answer 1

As the error message state, your left and right expressions have different size. You cannot do it in MATLAB.

To avoid for-loop you can use ARRAYFUN function:

rays = arrayfun(@(x) buildRay(particle, ((x-1).*anglePart, rayLength), 1:numRays);

Answer 2

You need to change buildRays to accept a vector (or matrix) of input arguments and return a matrix sized appropriately (ie not always 1x4 - if the input vector is N elements, return an Nx4 matrix).

Right now, you're trying to assign a 1x4 vector into a numRays x 4 spot - hence the error.