Help vectorize this matrix multiplication

[Jim Rockford]

I have a matrix M for which I want to multiply each row by a scalar,
which can be different for each row.

One way to do it is as follows. Suppose the set of scalars are put
into a vector v. Then

diag(v) * M

effects this multiplication.

In my case, the problem is that constructing the diagonal matrix
diag(v) will exceed my computer memory. Obviously I could resort to a
loop, but I'm wondering if there is a different way to vectorize this
multiplication.

Thanks,
Jim

[Nasser M. Abbasi]

What is wrong with just using bsxfun for this? (I do not understand
why you have to make a new matrix for).

EDU>> A=[1 2 3;4 5 6;7 8 9]

1 2 3
4 5 6
7 8 9

EDU>> v=[1 2 3]'
1
2
3

EDU>> bsxfun(@times,v,A)

1 2 3
8 10 12
21 24 27

--Nasser

[Matt J]

"Nasser M. Abbasi" <n...@12000.org> wrote in message <iu3nkr$o40$1...@speranza.aioe.org>...

>
>
> What is wrong with just using bsxfun for this? (I do not understand
> why you have to make a new matrix for).

====================

Or, you could use a sparse diagonal matrix instead of a full one

N=length(v);
spdiags(v(:),0,N,N)*M;

[Jim Rockford]

On Jun 25, 12:19 am, "Nasser M. Abbasi" <n...@12000.org> wrote:
> What is wrong with just using bsxfun for this? (I do not understand
> why you have to make a new matrix for).

Thanks. There's nothing wrong with using bsxfun to do this. I was
unaware of that function, which is why I was posting. It works great.

Jim