[petsc-dev] Seeking Advice on Petsc Preconditioners to Try

[Mark F. Adams]

On Dec 29, 2011, at 8:24 PM, Dave Nystrom wrote:

> Mark F. Adams writes:
>> On Dec 29, 2011, at 12:51 PM, Dave Nystrom wrote:
>> 
>>> Jed Brown writes:
>>>> On Thu, Dec 29, 2011 at 11:15, Dave Nystrom <dnystrom1 at comcast.net> wrote:
>>>> 
>>>>> I have tried out -ksp_type cg -pc_type gamg -pc_gamg_type sa on my problem
>>>>> and am encouraged enough with the results that I would like to try taking
>>>>> the
>>>>> next step with using gamg.  Could you provide some advice on how to do
>>>>> that?
>>>>> I'm not sure how to provide the null space info you say is important.
>>>>> 
>>>> 
>>>> Are you solving a scalar or vector problem?
>>> 
>>> Both although the most challenging problem right now is one for a Hall matrix
>>> system that is block banded with 2x2 blocks.  Right now, I am just inputting
>>> the matrix into a petsc seqaij matrix.  
>> 
>> Thats fine, actually require.  Just call this:
>> 
>> ierr = MatSetBlockSize(Amat,3);      CHKERRQ(ierr);
> 
> Shouldn't it be
> 
> ierr = MatSetBlockSize(Amat,2);      CHKERRQ(ierr);
> 
> since I have 2x2 blocks.

yes

> 
>>> I guess I need to put it into a petsc
>>> block matrix but have not yet attempted to do that.  I'm not sure how much
>>> work is involved - I need to read the section in the users manual on that.
>>> 
>>> Anyway, I have 5 scalar systems and on vector system with 2x2 blocks.  I am
>>> interested in applying gamg to all of them to see how well it works.
>>> 
>> 
>> 
>