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using nested for loops

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Durgga Rajendren
Durgga Rajendren on 18 Apr 2011
Commented: Leon Barainsky on 17 Dec 2019
Hi, how to use nested for loops to multiply 2 matrices and make it work just like MATLAB operator? The function must work on matrices of any compatible size. I know what is nested for loops but in this case ,I dunno hw to apply it. Any help is much appreciated.Thanks.

Answers (1)

Andrei Bobrov
Andrei Bobrov on 18 Apr 2011
most unwise variant
function C = yourmtimes(A,B)
[m,namb] = size(A);
n = size(B,2);
C = zeros(m,n);
for ii = 1:m
for jj = 1:n
c1 = 0;
for k = 1:namb
c1 = c1 + A(ii,k)*B(k,jj);
end
C(ii,jj) = c1;
end
end
more
m = size(A,1);
n = size(B,2);
C = zeros(m,n);
for ii = 1:m
for jj = 1:n
C(ii,jj) = sum(A(ii,:).*B(:,jj).');
end
end
or
m = size(A,1);
n = size(B,2);
C = zeros(m,n);
for ii = 1:m
for jj = 1:n
C(ii,jj) = A(ii,:)*B(:,jj);
end
end
or
m = size(A,1);
n = size(B,2);
C = zeros(m,n);
nones = ones(n,1);
for ii = 1:m
C(ii,:) = sum(A(ii*nones,:).'.*B);
end
etc.
  1 Comment
Leon Barainsky
Leon Barainsky on 17 Dec 2019
None of them work for me, could there be something wrong with my matlab settings?

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