Matlab: Operations along the first dimension of a 3D array

Question

I have a 3D array M(d*d,m,n). For each d*d vector of M (ie 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!

Answer 1

尝试这个 -

N = reshape(sum(reshape(M,d,[])),d,m,n)

Answer 2

我可能没有正确理解问题，但这是您要寻找的吗？

N=squeeze(sum(reshape(M,[d,d,size(M,2),size(M,3)])))