[petsc-users] Difference between Block Jacobi and ILU?

[Justin Chang]

Thanks Satish,

And yes I meant sequentially.

On Wed, Jan 13, 2016 at 8:26 PM, Satish Balay <balay at mcs.anl.gov> wrote:

> On Wed, 13 Jan 2016, Justin Chang wrote:
>
> > Hi all,
> >
> > What exactly is the difference between these two preconditioners? When I
> > use them to solve a Galerkin finite element poisson problem, I get the
> > exact same performance (iterations, wall-clock time, etc).
>
> you mean - when you run sequentially?
>
> With block jacobi - you decide the number of blocks. The default is
> 1-block/proc
> i.e - for sequnetial run you have only 1block i.e  the whole matrix.
>
> So the following are essentially the same:
> -pc_type bjacobi -pc_bjacobi_blocks 1 [default] -sub_pc_type ilu [default]
> -pc_type ilu
>
> Satish
>
> > Only thing is I can't seem to use ILU in parallel though.
>
>
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