Matrix Multiplications (Altar Output Matrix Size)
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I have a matrix of 100x10 multiplied with a matrix of 1x10. I need to get 100x10 values out as the result. Currently i only get 1x10 values as the ans. How could i modify the terms accordingly?
for i=1:1:100
for k=1:1:10
c1 = data(i,k) * p(1:k);
end
end
Also, are there any "computationally efficient" alternatives to a for loop in this case?
Please Advise. Thanks!
2 个评论
Mischa Kim
2014-1-28
Hello Chockalingam, what exactly do you need to calculate? Do you want to multiply the 100x10 separately with each of the entries of the 1x10 to get 10 100x10's?
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David Sanchez
2014-1-28
A = rand(100,1); % place here your 100x10 matrix
B = rand(1,10); % place here your 1x10 matrix
C = A*B; % C is your 100x10 matrix
Mischa Kim
2014-1-30
OK, you mean something like:
A = [1 2; 3 4; 5 6];
b = [1 3];
C = zeros(size(A));
for ii = 1:length(A(:,1))
C(ii,:) = A(ii,:)'.*b';
end
where A,b,C correspond to your data,p,c matrices.
0 个评论
Jos (10584)
2014-1-30
编辑:Jos (10584)
2014-1-30
Your question is a little confusing. Do you intend to do element-by-element multiplication or matrix multiplication?
Assuming you're after element-by-element multiplication (c1(i,j) = data(i,j) x p(j), for i=1:100 and j=1:10) you can use bsxfun, as suggested by Andrei.
% small example
data = cumsum(repmat(1:3,4,1)) % a 4-by-3 matrix
p = [10 20 30] % a 1-by-3 vector
% engine
c1 = bsxfun(@times,data,p)
% check
i=2,j=3,isequal(c1(i,j), data(i,j) * p(j))
If this is not what you intended, clarify yourself ...
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