Apply function to every pair of columns in two matrices in MATLAB

Question

In MATLAB, I\'d like to apply a function to every pair of column vectors in matrices A and B. I know there must be an efficient (non for

Answer 1

Do you mean pairwise? So in a for-loop the function will work as scalar_val = func(A(i),B(i))?

If A and B have the same size you can apply ARRAYFUN function:

newvector = arrayfun(@(x) func(A(x),B(x)), 1:numel(A));

UPDATE:

According your comment you need to run all combinations of A and B as scalar_val = func(A(i), B(j)). This is a little more complicated and for large vectors can fill the memory quickly.

If your function is one of standard you can try using BSXFUN:

out = bsxfun(@plus, A, B');

Another way is to use MESHGRID and ARRAYFUN:

[Am, Bm] = meshgrid(A,B);
out = arrayfun(@(x) func(Am(x),Bm(x)), 1:numel(Am));
out = reshape(out, numel(A), numel(B));

I believe it should work, but I don't have time to test it now.

Answer 2

Try

na = size(A,1);
nb = size(B,1);
newvector = bsxfun(@(j,k)(func(A(j,:),B(k,:))),1:na,(1:nb)');

bsxfun performs singleton expansion on 1:na and (1:nb)'. The end result, in this case, is that func will be applied to every pair of column vectors drawn from A and B.

Note that bsxfun can be tricky: it can require that the applied function support singleton expansion itself. In this case it will work to do the job you want.