[petsc-users] newbie questions on preconditioner LU

[Ling Zou]

On Mon, Jan 28, 2013 at 12:43 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

>
> On Mon, Jan 28, 2013 at 1:36 PM, Ling Zou <lingzou80 at gmail.com> wrote:
>
>> I guess I got the impression that M is generally the same as A from
>> reading the manual.(PETSc Users Manual, Reversion 3.3, page 71, under 4.1
>> Using KSP)
>>
>> "Typically the preconditioning matrix (i.e., the matrix from which the
>> preconditioner is to be constructed), Pmat, is the same as the matrix that
>> defines the linear system, Amat; however, occasionally these matrices
>> differ (for instance, when a preconditioning matrix is obtained from a
>> lower order method than that employed to form the linear system matrix)."
>>
>
> I think you are getting confused by mixed notation. A PC in PETSc is an
> algorithm that takes a matrix (Pmat in the docs) and does some work to be
> able to apply an operation (named "M^{-1}" in your first email). This does
> *not* imply that M=Pmat, or that M is ever available or used, there is just
> a a linear operation named "M^{-1}".
>

Hmmm...it's getting more complicated now. I guess I need read the manual
more carefully and study the example codes more. By the way, could you
redirect me to an example code or a tutorial to understand this better?

Ling
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