Two arrays defining 2D coordinates, as array indices

Question

I have a 2D array, call it A. I have two other 2D arrays, call them ix and iy. I would like to create an output array whose elements are the elements of A at the index pairs provided by ix and iy. I can do this with a loop as follows:

for i=1:nx
    for j=1:ny
        output(i,j) = A(ix(i,j),iy(i,j));
    end
end

How can I do this without the loop? If I do output = A(ix,iy), I get the value of A over the whole range of (ix)X(iy).

Answer 1

A faster way is to use linear indexing directly without calling SUB2IND:

output = A( size(A,1)*(iy-1) + ix )

... think of the matrix A as a 1D array (column-wise order)