[petsc-users] DMMG preconditioner used in KSP

[Barry Smith]

  If you are using DMMGSetSNES you can do a similar thing. That is why there are two matrix arguments.

  Barry

On Sep 28, 2010, at 9:34 PM, Shao-Ching Huang wrote:

> Thanks Barry. I will look into DMMGSetKSP and your suggestions.
> 
> Shao-Ching
> 
> On Tue, Sep 28, 2010 at 7:13 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>> 
>>  If you are using DMMGSetKSP() then just have the third argument (func) compute A+B as the first matrix and A as the second matrix. Then the smoothing and coarse grid solve will
>> only use the A entries. That is A+B will be preconditioned with geometric multigrid applied to A.
>> 
>>   But, I suspect that you will do just as well using A+B.
>> 
>>   Barry
>> 
>> On Sep 28, 2010, at 8:19 PM, Shao-Ching Huang wrote:
>> 
>>> Hi
>>> 
>>> I can trying to solve a linear system
>>> 
>>> (A+B)x=b
>>> 
>>> where A is the standard finite difference Laplacian matrix and B has
>>> only a few elements (i.e. B's number of non-zero entries is much much
>>> smaller than A's).
>>> Is it possible to precondition by applying DMMG on A (like in ex34.c)
>>> in a KSP solver? Is there an example that I can follow to set this up?
>>> 
>>> Thanks,
>>> 
>>> Shao-Ching
>> 
>>