[petsc-dev] Performance of Petsc Cholesky vs LU

[Jed Brown]

On Wed, Nov 30, 2011 at 14:04, Barry Smith <bsmith at mcs.anl.gov> wrote:

> Ok, so how can we resolve this? The problem is that the default ordering
> is set when the PCCreate_Cholesky() and is set to be natural in order "to
> be safe" if sbaij matrix is used. We could change it to default to ND and
> then when PCSetUp_Cholesky() is called simply set the ordering to natural
> if it is a sbaij matrix. Kind of a hack but what do you suggest that
> doesn't involve tracking some other variable indicating if the user has set
> the ordering type to something else ...
>

Why the hell set it so soon? This is like choosing which side/norm to use
in a Krylov method. Make the decision lazily (when it is requested or
needed to do something), otherwise leave it undefined.
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