Matrix Multiplications (Altar Output Matrix Size)
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Chockalingam Kasi
il 28 Gen 2014
Commentato: Chockalingam Kasi
il 31 Gen 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 Commenti
Mischa Kim
il 28 Gen 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?
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Più risposte (3)
David Sanchez
il 28 Gen 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 Commento
Mischa Kim
il 30 Gen 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 Commenti
Jos (10584)
il 30 Gen 2014
Modificato: Jos (10584)
il 30 Gen 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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