Add / subtract / multiply / divide matrix by vector along defined dimension

Hi,

I have a matrix A with the size [5 11 4 11] and a vector B with the size [4]. I want to divide the matrix by the vector by the third dimension of the matrix, in a way, that

for i = 1:4

C(:,:,i,:) = A(:,:,i,:) / B(i);

end

The same I want with subtracting. Is there a better, predefined way, than using a loop? Preferaed would be a function, which has the dimension as a parameter, such as

Example: C = divdim(A,B,3);

Thank you

Answer 1

[Jan]

A = rand([5, 11, 4, 11]);
B = rand([4, 1]);  % Or [1, 4]? "[4]" is no valid size in Matlab

C = A ./ reshape(B, [1, 1, 4, 1]);  % Note: ./ , not /
D = A -  reshape(B, [1, 1, 4, 1]);
...

This works since R2016b, when the auto-expanding was introduced. With older Matlab versions you need bsxfun.

You can omit the trailing 1's in the dimension, so this is sufficient already:

E = A +  reshape(B, [1, 1, 4]);