matrix multiplication in matlab

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vasantha malairamar
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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回答（1 个）

Jan
Jan 2017-3-29
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;
  2 个评论
Rik
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.
Jan
Jan 2017-3-29
@Rik: disp works well with numbers and arrays:
x = rand(2)
disp(x)

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