how can i simplify this expression

Question

Dror Aizik 2020-4-8

0
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https://ww2.mathworks.cn/matlabcentral/answers/516292-how-can-i-simplify-this-expression

评论： Dror Aizik 2020-4-10

采纳的回答： David Goodmanson

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u is 37x37x37x37 complex matrix

h is 37*37 complex matrix

i want to simplify this expression:

N=37;
res=zeros(N,N,N,N);
for i=1:N
    for j=1:N
        res(:,:,i,j)=h(i,j)*u(:,:,i,j);
    end
end
    res=sum(res,[3 4]);

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Ameer Hamza 2020-4-8

I guess the for loop is already the simplest way you can do it.

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Answer 1

David Goodmanson 2020-4-9

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Hi Dror,

n1 = 10;  % in case the dimensions are not all the same
n2 = 6;
n3 = 33;
n4 = 28;
u = rand(n1,n2,n3,n4) + i*rand(n1,n2,n3,n4);
h = rand(n3,n4) + i*rand(n3,n4);
res = zeros(n1,n2,n3,n4);
for ii = 1:n3    % I don't use i as a sum variable so i can stay as sqrt(-1) 
    for j = 1:n4
        res(:,:,ii,j)=h(ii,j)*u(:,:,ii,j);
    end
end
res = sum(res,[3 4])
% different way
uu = reshape(u,n1*n2,n3*n4);
hh = reshape(h,n3*n4,1);
res1 = reshape(uu*hh,n1,n2)     % same thing