[Scilab-users] multiple element by element between large matrix and vector

[Tim Wescott]

On Sun, 2015-09-27 at 13:43 +0200, Samuel Gougeon wrote:
> Hi David,
> 
> Le 27/09/2015 12:53, David Chèze a écrit :
> > Hi all,
> >
> > I was wondering what are the possibilities to do a product element by
> > element between a matrix A (m rows ,n columns)and a vector (let say column
> > vector v (m elements) ): I want each element of each column of A to be
> > multiplied by each element of v at the same row. What I'm using for now is a
> > product by a diagonal matrix based on v. For large matrix in data
> > manipulation (typ. 100000 rows), it's necessary to use sparse to allocate
> > better the diag matrix otherwise it's out of memory for usual machine.
> > So i'm using --> diag(sparse(v)) * A
> >
> > Have you best practise to share on this topic ?
> .
> I am not sure to catch what you want to do, noticeably what is the 
> format of the result you expect.
> AFAIU, i would do
> A .* (v*ones(1,size(A,2)))

"Otherwise it's out of memory for usual machine"

Meaning, he tried that, and it didn't work.  So he does what DOES work,
which is

diag(sparse(v)) * A

This makes the matrix on the left sparse, with a populated diagonal and
all the rest zeros (presumably v is fully populated).  And, as David has
discovered experimentally, it does not run him out of stack space.

-- 

Tim Wescott
www.wescottdesign.com
Control & Communications systems, circuit & software design.
Phone: 503.631.7815
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