Matrix Multiplication with its transpose in the loop

Hi,

Let's say I have a matrix

A = [1 2 3 4 5
     2 3 4 5 6
     3 4 5 6 7
     4 5 6 7 8]

I need to do matrix multiplication i.e. A'*A, but not all the rows and the column at once. For example, I want to multiply the first two column of the matrix first and obtain a result (let's say r1), then column 1, 2 and 3 multiplied with its transpose, obtain the result (let's say r2) and then column 1,2,3, and 4 multiplied with its transpose and the result is r3 and so on. I have to save the result in the matrix, let's say B

B = [r1 0 0 0 
     r1 r2 0 0
     r1 r2 r3 0
          .....]

Can anyone help me with this?

Thank you!

[John Chilleri]

A simple solution might just be to program matrix multiplication with some for loops and selectively store values.

[David Goodmanson]

Hi MD, Is there some kind of extra summation that you are not mentioning? If you take, say, a 10x10 matrix and multiply three columns worth of that by its transpose, then depending on which order you do the multiplication the result is either 10x10 or 3x3. In neither case is the result a scalar, as appears to be the case with matrix B.

[Mystery Devil]

Hey John, I know I should use the loop, but that's what I am trying to figure out. I don't know how to loop it

[Mystery Devil]

Hi David, please see the below link for full description and how I want the data to be stored:

http://www.mathworks.com/matlabcentral/answers/321435-matrix-multiplication-to-find-unknowns-in-a-loop

Thanks a lot!

Answer 1

[Walter Roberson]

   for k=1:size(A,2)
     T=A(:, 1:k);
     B{k} = T'*T;
    end