Re: large sparse matrix

[Carlo de Falco]

On 31 Aug 2009, at 17:23, dbateman wrote:

> Its not a bug.. Trying to factorize a sparse random matrix invariably
> results in a dense factorization... You need some structure in the  
> original
> sparse matrix that the factorization can use to keep the factorization
> sparse...  A 20e3-by-20e3 dense matrix is much larger than both the  
> 32bit
> limit of 2Gvalues and 4GB..
>
> Try using some of the test matrices from the Florida University sparse
> matrix collection instead as these matrices are derived from real  
> problems
> and have structure that the factorization can use to keep the matrix  
> sparse.
>
> Regards
> David

David,
Thanks for the quick answer!
I understand now that the matrix I used in the previous email was not  
a good example...
Though, the matrix that produced the problem in the first place comes  
from a Galerkin discretization
of Stokes' equation, so it does have a very precise structure, it is  
essentially of the form

[A B' 0; B 0 E'; 0 E 0]

where A and B are banded, E is a row vector and A is SPD.
Also, I tried to save the matix and rhs and solve the system in matlab  
and it worked fine on the same hardware.
I find this particularly puzzling as I thought that both matlab aand  
Octave ultimately rely on
SuiteSparse for solving Sparse linear systems...

c.