MATLAB: Sigma Multiple Matrix for Loop

for loopmatrixsigma

Hi, I have a question. I wanna write code for matlab with this formula.
I confused in loop. My code:
A = [ 0.1 0.2 0.3 0.4
      0.4 0.5 0.6 0.7
      0.8 0.9 1.0 1.0
      0.8 0.9 1.0 1.0];
[i,h]=size(A);
B = [ 0 1 0 1 0 1
    1 0 0 1 0 0
    0 0 1 1 0 0
    1 0 0 0 0 1];
[h,j]=size(B);
mat=zeros(i,j);
temp=zeros(i,j);
for c=[1:j]
  for r=[1:i]
      temp(r,c)=A(r,r)*B(r,c);
      mat=mat+temp;
  end
end
I'm not sure of this code, is this right?

Best Answer

"is this right?"
No.
The formula is for basic matrix multiplication, so you can just use the inbuilt and very efficient mtimes:
A*B
If you really want waste time writing nested loops, then try this:
A = [ 0.1 0.2 0.3 0.4
      0.4 0.5 0.6 0.7
      0.8 0.9 1.0 1.0
      0.8 0.9 1.0 1.0];
B = [ 0 1 0 1 0 1
    1 0 0 1 0 0
    0 0 1 1 0 0
    1 0 0 0 0 1];
S = [size(A,1),size(B,2)];
D = nan(S);
for ii = 1:S(1)
    for jj = 1:S(2)
        tmp = 0;
  for k = 1:size(A,2)
      tmp = tmp+ A(ii,k)*B(k,jj);
  end
  D(ii,jj) = tmp;
    end
end
disp(D)   % nested loops
disp(A*B) % simpler and much more efficient
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