Matrix Multiplications (Altar Output Matrix Size)

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!

[Mischa Kim]

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?

[Chockalingam Kasi]

Hi Mischa!

not exactly.. i want all elements in the (100x10) matrix to be multiplied with the (1x10) matrix.

Like each Row of the (100x10) to be multiplied with the (1x10) and finally i will get an output of (100x10).

Thanks!

Answer 1

[Andrei Bobrov]

c1 = bsxfun(@times,A,B);

[Chockalingam Kasi]

Hi Andrei & mischa.. thanks!

For the bsxfun i get this error since my dimensions do not match-up "Non-singleton dimensions of the two input arrays must match each other."

My Matrix dimensions are "(100x10) x (1x10)".. In essence i want to multiply all 100 rows of the 1st matrix with the 2nd matrix individually. In the end i need a matrix of (100x10).

Cheers!

Answer 2

[David Sanchez]

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]

Hello David, his first matrix is a 100x10. Yours is a 100x1.

Answer 3

[Mischa Kim]

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.

Answer 4

[Jos (10584)]

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 ...

[Chockalingam Kasi]

Hi Jos! Thanks much!

Cheers!