Operations along the first dimension of a 3D array

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f10w
f10w 2014-5-29
编辑： Matt J 2014-5-29
I have a 3D array M(d*d,m,n). For each d*d vector of M (i.e. vectors of the first dimension), I split it into d parts and take the sum of each part to form a new vector (of size d). For example, if u is a vector along the first dimension of M, then it will be replaced by the vector v, computed by:
v = sum(reshape(u,d,d))';
For the moment I use a loop as following, but I think there should be a much faster way to do it.
N = zeros(d,m,n)
for i=1:m
for j=1:n
N(:,i,j) = sum(reshape(M(:,i,j),d,d))';
end
end
Thank you so much for any suggestions!

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Matt J
Matt J 2014-5-29
编辑：Matt J 2014-5-29
Looks like M should have been a 4D array from the beginning,
M=reshape(M,d,d,m,n);
N=sum(M,2);
  1 个评论
Matt J
Matt J 2014-5-29
编辑：Matt J 2014-5-29
Khue Commented:
Thanks. But N=sum(M,2) will give a 4D array, right? I got this answer:
N = squeeze(sum(reshape(M,d,d,m,n)))
The idea is the same as yours.
Thanks again.

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