CODEWITHSUNDEEP
arraysmatlabvectorizationmatrix-multiplication
obchardon
obchardon

Reputation: 10790

Multiplying matrix along one specific dimension

QUESTION

I'm looking for an elegant way to multiply two arrays along one particular dimension.

SIMILAR QUESTION

There is already a similar question on the official matlab forum, but the thread is outdated (2004).

EXAMPLE

M1 a [6x4x4] matrix and M2 a [6x1] matrix, I would like to multiply (element by element) M1 with M2 along the 3rd dimension of M1 to obtain a matrix M [6x4x4]

An equivalent to:

M1 = rand(6,4,4);
M2 = rand(6,1);

for ii = 1:size(M1,2)
   for jj = 1:size(M1,3)
      M(:,ii,jj) = M1(:,ii,jj).*M2;
   end
end

VISUAL EXAMPLE

multiplication along one particular dimension

Do you know a cool way to do that ? (no loop, 1 or 2 lines solution,...)

Upvotes: 1

Views: 705

Answers (1)

rayryeng
rayryeng

Reputation: 104555

If I'm interpreting your question correctly, you want to take each temporal slice (i.e. 1 x 1 x n) at each spatial location in M1 and element-wise multiply it with a vector M2 of size n x 1. bsxfun and permute are perfect for that situation:

M = bsxfun(@times, M1, permute(M2, [2 3 1]));

Upvotes: 4

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