Re: Applying each element of a vector to each row of a matrix

[Martin Helm]

Am Sonntag, 19. Dezember 2010, 16:33:20 schrieb Jordi Gutiérrez Hermoso:
> I'm often found with a situation in which I have some matrix A and
> some vector v and I would like to do something like multiply each
> column or row in A by each element of v. I've wished that something
> like A.*v or v.*A would do this if the row or column dimensions of A
> matched those of v, but of course this doesn't work. I end up
> resorting to repmat instead to turn v into a matrix whose dimensions
> match those of A.
> 
> My questions are, is there another way to do this more cleanly without
> first calling repmat? If there isn't, would this be a reasonable
> extension of the elementwise operators?
> 
> Thanks in advance,
> - Jordi G. H.
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There is a special type "diagonal matrix" which should fit your needs.
with diag(v) you create a diagonal matrix which behaves like a matrix and can 
be used to scale rows/columns without the overhead of creating a full matrix 
(and a corresponding full matrix multiplication), but only in newer octave 
versions, I do not remember when it was introduced.

diag(v)*a for example