CODEWITHSUNDEEP
matlabmatrix-multiplicationelementwise-operations
skr
skr

Reputation: 452

Elementwise multiplication of a matrix by a vector

Suppose I have a matrix A=rand(2,14,24) and a vector x=10*ones(1,14)

I want element wise multiplication of A and x, such that B(i,j,k)=A(i,j,k)*x(j) for all j=1,2,..14. I want to be able to do this without running a loop. What is the most efficient way to do this in matlab?

Upvotes: 1

Views: 4454

Answers (2)

Eitan T
Eitan T

Reputation: 32920

If you're multiplying A by a vector of 10's element-wise, wouldn't it be easier to simply multiply by a scalar instead?

B = A * 10;

For a general case, there is no need for repmat logic here. bsxfun can do the trick (and it's faster). :

B = bsxfun(@times, A, x);

Upvotes: 7

Ansari
Ansari

Reputation: 8218

You first use repmat to tile x the right number of times, then do element-wise multiplication.

repX = repmat(x, [size(A, 1), 1, size(A, 3)]);
B = A.*repX;

Upvotes: 1

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