Thread Subject: looping/vectorising issue...

Anyone have any suggestions on how to vectorise this loop? (by vectorise, i guess i mean converting to matrix multiplication)

I'm at a loss!

dimensions are:
z1(m,n)
z2(m,k)
z3(m,n*k)

for i=1:size(z1,1)
    z3(i,:)=reshape(z1(i,:)'*z2(i,:),1,[]);
end



thanks heaps!

"Rich " <richardwood@removethishotmail.com> wrote in message <gn0vhg$rn$1@fred.mathworks.com>...
> Anyone have any suggestions on how to vectorise this loop? (by vectorise, i guess i mean converting to matrix multiplication)
>
> I'm at a loss!
>
> dimensions are:
> z1(m,n)
> z2(m,k)
> z3(m,n*k)
>
> for i=1:size(z1,1)
> z3(i,:)=reshape(z1(i,:)'*z2(i,:),1,[]);
> end
>
> thanks heaps!

 [I,J] = ndgrid(1:n,1:k);
 z3 = z1(:,I).*z2(:,J);

Roger Stafford

thanks Roger, you are a legend, and have saved me 75% of my runtime!

So I hit memory problems as soon as I do this for big matrices (thousands by thousands), maybe I should have mentioned that before.
So, does anyone have a less memory intensive version?

I am generally working with sparse matrices, so I think I have to kick my brain into gear enough to work out how to use the find command in this context. But any pointers would be much appreciated!

thanks

On 18 Jun, 13:40, "Rich " <richardw...@removethishotmail.com> wrote:
> So I hit memory problems as soon as I do this for big matrices (thousands by thousands), maybe I should have mentioned that before.
> So, does anyone have a less memory intensive version?

That's the problem with 'vectorization': You gain some speed at
the expense of memory.

If you're hitting the memory wall, you have two options:

1) Buy a bigger computer.
2) Implement a MEX routine in C or C++.

Rune