I have n groups, each group has m vectors of dimension d. These are represented by ad*m*n matrix A.
I have n vectors of dimension d, represented by ad*n matrix B.
Now I would like to subtract all the m vectors in the group i by the corresponding vector i in B (and I do that for all i = 1,...,n).
This can be done simply like:
C = zeros(size(A));
for i = 1:n
for j = 1:m
C(:,j,i) = A(:,j,i) - B(:,i);
end
end
However, this is quite slow because of the loop. Could anybody please suggest me a very fast way to do that?
Thank you in advance for your help.
bsxfun
完美案例 -
C = bsxfun(@minus,A,permute(B,[1 3 2]))
Give this a shot:
B = repmat(reshape(B,[d 1 n]),[1 m 1]);
C = A - B;
EDIT
Divakar's solution is faster. For 100 runs with d=50;m=75;n=100; the average times were as follows:
Nesbit's - .0165s
Divakar's - .0013s
Mine - .0023s
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