Re: RE: Filling sparse matrix by A(i, i)=... .Fast for small matrices, slow for large.Is there a better way to fill the matrix?

Well.. 
Try to allocate/deallocate memory rarely.

How about that :
Try to use std::vector<> with sparse mtl matrix
and allocate memory not every entry you made 
but say every 1000 entries :


--------------------------
 std::vector<..> a;
 int mem =  /* 10^5 is also good */ 1000 ;
 a.reserve( mem );
 
// put matrix entries, some loop :
{
           a.push_back(some_entry)

           if( a.size()>= a.capacity() ) 
           { 
            mem+=1000;
            a.reserve(mem);
           }
}
// end loop
--------------------





and finally build up a sparse matrix :)

JO













 --- Guilherme Parreira <[email protected]> wrote:

> 
> Thanks, JO.
> 
> It happens that I don't know a priori how many
> non-zero elements the matrix
> will contain.
> 
> Regards,
> ==============================
> Eng. Guilherme F. Parreira
> Electrical Engineering Graduate Student
> GOPAC - UFMG - Brazil
> ==============================
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On
> Behalf Of Janusz opechowski
> Sent: terça-feira, 26 de abril de 2005 09:19
> To: General Matrix Template Library (MTL) list
> Subject: Re: MTL: RE: Filling sparse matrix by
> A(i,i)=... .Fast for small
> matrices,slow for large.Is there a better way to
> fill the matrix?
> 
> Hi there,
> try using previously allocated memory.
> 
> Everytime you add some value probably memory is
> allocate one more time  
> ( .. how about std::vector<T>.reserve() mechanism 
> dear sirs )
> 
> 
> Beautifull exampe of it is in MTL's 
> online example file.
> 
> Go there :
> 
>
http://www.osl.iu.edu/research/mtl/show_src.php3?file=./examples/sparse_matr
> ix.cc
> 
> Cheers.
> JO
> 
> 
>  --- Guilherme Parreira <[email protected]>
> wrote:
> 
> > The MTL documentation says to use iterators in
> order
> > to speed up computation
> > in matrices, but I don't know how.
> > 
> > Regards, 
> > ==============================
> > Eng. Guilherme F. Parreira
> > Electrical Engineering Graduate Student
> > GOPAC - UFMG - Brazil
> > ==============================
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]] On
> > Behalf Of Tony
> > Sent: domingo, 24 de abril de 2005 10:23
> > To: [email protected]
> > Subject: MTL: Filling sparse matrix by A(i, i)=...
> > .Fast for small
> > matrices,slow for large.Is there a better way to
> > fill the matrix?
> > 
> > Hi
> > 
> > I have a sparse matrix
> > 
> > #define N   10000
> > 
> > typedef matrix< Type, 
> >   rectangle<>, 
> >   compressed<>,
> >   row_major >::type Matrix;
> > 
> > Matrix A(N,N);
> > 
> > and I am filling it up something like
> > 
> > for(i=0; i < N ; i++){
> >     A(i,i) = ....
> >        lots of other stuff in here setting up
> other
> > elements of A 
> >     
> > }
> > 
> > In my case I have quite a complex set of if
> > statements in the loop
> > setting up the A matrix and I have a maximum of 12
> > non zero entries on
> > each row.
> > 
> > The code works fine for small matrix sizes, say N
> > less than 50,000. 
> > But when I set N larger than this the code runs
> very
> > slowly.  In my
> > case I would like to run the code with N=1500000. 
> > But I need to leave
> > the computer on for several days for A to be
> > constructed.
> > 
> > Question:
> > Can I fill the elements of A in a faster way?  I
> am
> > wondering if if
> > would be faster adding a whole row at a time to A,
> > but I don't know
> > how to do this, if this is a possibility can
> someone
> > please show me
> > how to do this and/or any other ways I can speed
> up
> > filling up the
> > elements of A
> > 
> > Thank you for your time
> > 
> > Tony
> > 
> > _______________________________________________
> > This list is archived at
> > http://www.osl.iu.edu/MailArchives/mtl-devel/
> > 
> > 
> > 
> > _______________________________________________
> > This list is archived at
> > http://www.osl.iu.edu/MailArchives/mtl-devel/
> >  
> 
>
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