Fastest way to multiply each block of an array with another matrix

Hello all,

I have a 12x4xN array which I would like to multiply each 12x4 block by a 4x16 matrix in order to get a 12x16xN array. Could somebody please help me with a fast way of doing that? Thank you!

Answer 1

[James Tursa]

If you have a C compiler:

A = your 12 x 4 x N array;
B = your 4 x 16 matrix;
out = mtimesx(A,B);

You can find mtimesx here:

http://www.mathworks.com/matlabcentral/fileexchange/25977-mtimesx-fast-matrix-multiply-with-multi-dimensional-support

If you don't have a C compiler, then you can try MULTIPROD:

http://www.mathworks.com/matlabcentral/fileexchange/8773-multiple-matrix-multiplications--with-array-expansion-enabled

[Mnr]

Thank you! I did it using mltiprod and it is perfect. Can I know what is the best way to install the C compiler as well?

Answer 2

[Andrei Bobrov]

Let A - your array with size [12x4xN]

B - matrix 4x16

sa = size(A);
sb = size(B);
out = zeros([sa(1),sb(2),sa(3)]);
for jj = 1:sa(3)
    out(:,:,jj) = A(:,:,jj)*B;
end

[Mnr]

Thank you!