[petsc-dev] Performance of Petsc Cholesky vs LU

[Barry Smith]

On Nov 30, 2011, at 1:47 PM, Jed Brown wrote:

> On Wed, Nov 30, 2011 at 13:38, Barry Smith <bsmith at mcs.anl.gov> wrote:
> Jed if you know how to do efficient Cholesky with nd ordering using the sbaij data structure that would be a great addition to PETSc but I think it is likely impossible.
> 
> You can build the column-oriented indices or just make a copy. I don't know what CHOLMOD and MUMPS do, but even a full copy followed by factorization in the new natural ordering isn't going to be a big deal. We wouldn't need iterative solvers at all if direct solvers had a fill factor of order one.

  Right, so why not just use the AIJ format if you plan to use a direct Cholesky solver; only the upper triangular part of the factor is actually stored so the memory usage of AIJ for Cholesky is just the same as as of SBAIJ for Cholesky.,


   In other words, if you want to use full Cholesky just use AIJ.

   Barry