matrix multiplication in matlab

Question

vasantha malairamar 2017-3-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/332444-matrix-multiplication-in-matlab

评论： Jan 2017-3-29

XYZ=[0.5141 0.3239 0.1604;0.2651 0.6702 0.0641;0.0241 0.1228 0.8444];
  for i=1:768
      for h=1:768
         nf=mR(i,h);
         fd=mG(i,h);
         gs=mB(i,h);
       bv=[nf fd gs];
       hd=bv';
       disp(hd);
        mmul=double(hd).*XYZ;
       disp(mmul);
      end
  end

Error using .* Matrix dimensions must agree.

Error in Untitled6 (line 22) mmul=double(hd).*XYZ;

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Answer 1

Jan 2017-3-29

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All we see is the failing code, and we have to guess its intention. Better explain this to get the solution you want.

double(hd) .* XYZ
[3 x 1]    .* [3 x 3]

Do you want the result to be [3 x 3]? This works in Matlab >= 2016b with automatic expanding. With older versions, the elementwise multiplication demands for two arguments of the same size. Then:

mmul = bsxfun(@times, double(hd), XYZ);

or

mmul = double(hd(:, [1,1,1]) .* XYZ;

But perhaps you want a matrix multiplication?

mmul = double(bv) * XYZ;

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Rik 2017-3-29

Also: you should convert numbers to strings before using disp. You can use fprintf, a combination of sprintf and disp, or a combination of num2str and disp. I strongly advise the first.