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

In MATLAB, I would like to apply a function to each pair of column vectors in matrices A

and B

. I know there must be an efficient (not for

) way to do this, but I cannot figure it out. The function will output a scalar.

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2 answers


Try

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


bsxfun

performs one-color expansion by 1: na and (1: nb) '. The end result in this case is that func will be applied to every pair of column vectors taken from A and B.

Note that bsxfun can be tricky: it may require the application function to support singleton expansion. In this case, it will work to get the job done.

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Do you mean in pairs? So during the loop, the function will work like scalar_val = func(A(i),B(i))

?

If A

both B

are the same size, you can use the ARRAYFUN function :

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

UPDATE

As per your comment, you need to execute all combinations of A and B as scalar_val = func(A(i), B(j))

. This is a little more complicated and for large vectors it can fill up memory quickly.



If your function is 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.

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