Hi.I want to multiply n matrices with k,k+1 dimension and the problem is that if I test the code on paper it seems right but written on matlab well it's a little bit different. here is the code :

Hi. I want to multiply p matrices with k,k+1 dimension and the problem is that if I test the code on paper it seems right, but written in matlab, well, it's a little bit different. Here is the code :

for k=1:p-1  
  for i=1:size(A{k+1},2)
    R(1,i)=0;
    for j=1:size(A{k},2)      
      R(1,i)=R(1,i)+A{k}(1,j)*A{k+1}(j,i);
      A{k+1}(1,i)=R(1,i);      
    end
  end
end
R

Would you please take a look and tell me, if you can, what's wrong?

Because if I check R with A1*A2*A3 for example they are not the same. And they should...

Thank you.

[Image Analyst]

What are A, A1, A2, and A3? What does "matrices with k,k+1 dimension" mean? Just tell us how many rows and columns it has. From the looks of it, it looks like A is a cell array - either a column vector of cells or a row vector of cells. Why is it a cell array?

[Beatrice Rotaru]

If p=3 then I will have 3 matrices : A1,A2 and A3. Each one will have k rows and k+1 columns so if k starts with 1 the product of the matrices will be a vector

[Beatrice Rotaru]

I used this to generate the A's randomly and in order

for k=1:p

A{k} = rand(k,k+1);

end

[Roger Stafford]

If A1 and A2 each have k rows and k+1 columns, then A1*A2 is an invalid matrix multiplication, because A1 must have the same number of columns as A2 has rows. Of course the same difficulty pertains to A1*A2*...*An when they each are k by k+1 in size.

Answer 1

[Roger Stafford]

All you are going to get with this computation is the first row of the product of these A{...} matrices. The result will therefore of course not agree with the full product. To do the for-loop type computation you are using, you would need to have them four deep instead of three to get all rows.