Question regarding PCMG

[TsuyoshiKoyama(berkeley)]

With regards to the first problem I had, I was misinterpreting how
the function PCApply should work. I had assumed that you could pass
in an initial vector x_init to the PCApply by calling PCApply(x, x_init) and 
have x_init
rewritten by the result. Unfortunately this is not the correct way to do 
things
in PETSc and I have figured out a way to use the KSPRichardson context
for the stationary solver I have coded as my own PC object.

For the second problem, the fix for the first problem will avoid it since I
will no longer be trying to use the KSPPreonly but the KSPRichardson.

Thank you very much for your help, Mr. Knepley!

Sincerely,

-Tsuyoshi Koyama

----- Original Message ----- 
From: "Matthew Knepley" <knepley at gmail.com>
To: <petsc-users at mcs.anl.gov>
Sent: Tuesday, August 14, 2007 3:02 PM
Subject: Re: Question regarding PCMG


> On 8/13/07, TsuyoshiKoyama(berkeley) <tkoyama at berkeley.edu> wrote:
>> As for the second case, the reason I might not select a coarse solver is
>> since I
>> am trying to solve a Helmholtz equation and the coarse grid solve might 
>> not
>> be
>> correct enough to apply. Thus, you may just point out that the coarse 
>> grid
>> should
>> be large enough to resolve the so called low frequency error and that if 
>> you
>> do so
>> you should still be able to solve direct, but I was curious on testing
>> different types
>> of operations at the coarsest level.
>
> The coarse solver can be set to anything you choose. You just extract the
> coarse KSP and set the type.
>
>  Thanks,
>
>    Matt
>
> -- 
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which
> their experiments lead.
> -- Norbert Wiener
>