Matrix Multiplications (Altar Output Matrix Size)
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Chockalingam Kasi
on 28 Jan 2014
Commented: Chockalingam Kasi
on 31 Jan 2014
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 Comments
Mischa Kim
on 28 Jan 2014
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?
Accepted Answer
More Answers (3)
David Sanchez
on 28 Jan 2014
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
1 Comment
Mischa Kim
on 30 Jan 2014
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 Comments
Jos (10584)
on 30 Jan 2014
Edited: Jos (10584)
on 30 Jan 2014
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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