How to use a loop to calculate m*n values for an mxn matrix?
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I have two matrices, both approximately 100x100, call them A and B. I am trying to multiply every element of matrix A by every element of matrix B and output these values to a third matrix. In reality, I am doing a little bit more than multiplication, but the operation itself isn't my problem. I am having trouble figuring out how to organize this within a loop.
Any suggestions are greatly appreciated!
1 个评论
Jan
2013-9-27
As usual it would be helpful, if you post, what you have tried so far an explain, which problems occur.
采纳的回答
So you want to multiply 10'000 elements of A with all 10'000 elements of B such that you get 100'000'000 elements as result?
C = zeros(1, 100000000); % 1e8
iC = 0;
for iA = 1:10000
for iB = 1:10000
iC = iC + 1;
C(iC) = A(iA) * B(iB);
end
end
If this is what you are searching for, omitting the inner loop is most likely faster:
B = B(:);
C = zeros(10000, 10000); % 1e8 elements
for iA = 1:10000
C(:, iC) = A(iA) * B;
end
end
And then the relation to BSXFUN is more obvious, but this might be much more complicated in your real case:
C = bsxfun(@times, A(:).', B(:));
If you explain "a little bit more than multiplication" in detail, it would be clear if BSXFUN would be applicable. But perhaps you can use the example as pattern for the more complicated calculations already.
更多回答（1 个）
Ilham Hardy
2013-9-27
编辑：Ilham Hardy
2013-9-27
Is it something like this?
A = [1 2 3 4; 5 6 7 8; 9 10 11 12];
B = [2 2 2 2; 3 3 3 3; 4 4 4 4];
>> C = A.*B
C =
2 4 6 8
15 18 21 24
36 40 44 48
2 个评论
Ilham Hardy
2013-9-27
Sorry, i didn't read your question carefully.
Could you elaborate more on the "a little bit more than multiplication" -part?
Perhaps a simple example of your matrix and the operation?
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