[petsc-users] parallel Mat Mult a serial Vec or a serial Mat

[Jed Brown]

On Sun, Jan 20, 2013 at 1:06 PM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:

> Thanks very much! I am taking a look of this example.  But MATNEST does
> not support factorization.
> I understand now I must do it in a basic way using MatSetValuesLocal.
>

With that example, you run with -dm_mat_type nest if you want to use
MATNEST, acknowledging that it means you'll be using a fieldsplit
preconditioner. Note that the term "nest" does not appear anywhere in the
code. Without that option, an AIJ format will be used, so you can use a
direct solver or anything else. MATNEST here is a run-time optimization
that is primarily only useful for fieldsplit (or shell) preconditioning.
It's a very bad idea to make your code depend on MATNEST because it
severely limits your choices of algorithms.
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