[petsc-users] Two PCs on same residual in multiplicative fashion !

[Abdul Hanan Sheikh]

Yes, it sounds crazy when we look exclusively at this. But I do not do this exclusively. 

Basically,  this happening [ P1^{-1} P2^{-1} A x = P1^{-1} P2^{-1} b ] occurs as a part of my two-level solver. 

Any how I have to do this. 


I had a realization, PCCOMPOSITE does not do exactly what I want. I read about PCCOMPOSITE in manual. :( 


Thanks, 

Abdul 





>________________________________
> From: Matthew Knepley <knepley at gmail.com>
>To: Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk>; PETSc users list <petsc-users at mcs.anl.gov> 
>Sent: Friday, 26 October 2012, 18:56
>Subject: Re: [petsc-users] Two PCs on same residual in multiplicative fashion !
> 
>
>On Fri, Oct 26, 2012 at 12:45 PM, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk> wrote:
>
>Thank you Matt, your assumption is alright. It was typo. 
>>
>>I got this idea , yet if I want to invert P2 exactly by PCLU then how should I do ?? 
>
>
>Read this: http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCKSP.html
>
>
>This makes things more complicated. You can use PCOMPOSITE with multiplicative, but its not
>exactly what you have written. This is never used because its not really effective, and doesn't make
>much sense from a theory perspective. Are you sure you want to do this?
>
>
>    Matt
>
>
>This is indeed, but I avoid to merge(matrix product) for some reasons. 
>>
>>
>>
>>Thanks again. 
>>
>>Abdul
>>
>>
>>
>>
>>>________________________________
>>> From: Matthew Knepley <knepley at gmail.com>
>>>To: Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk>; PETSc users list <petsc-users at mcs.anl.gov> 
>>>Sent: Friday, 26 October 2012, 18:22
>>>Subject: Re: [petsc-users] Two PCs on same residual in multiplicative fashion !
>>> 
>>>
>>>On Fri, Oct 26, 2012 at 12:04 PM, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk> wrote:
>>>
>>>
>>>>
>>>>Dear Developers and members, 
>>>>
>>>>
>>>>
>>>>I intend to solve system Ax=b with two preconditioners as follows: 
>>>>
>>>>
>>>>
>>>>P1^{-1} P2^{-1} A x = P^{-1} P^{-1} b
>>>
>>>
>>>I assume you mean P1^{-1} P2^{-1} A x = P1^{-1} P2^{-1} b
>>>
>>>
>>>
>>>
>>>With this setup, I think its easiest to use PCKSP with the matrix for
>>>the KSP being P2. That would give you
>>>
>>>
>>>  P2^{-1} A x = P2^{-1} b
>>>
>>>
>>>Now you can precondition that solve with another PCKSP with the matrix
>>>for that KSP being P1, and get what you want.
>>>
>>>
>>>This seems like a strange thing since you could just merge those matrices.
>>>
>>>
>>>   Matt
>>> 
>>>where P1 and P2 are exclusively available as matrices. 
>>>>
>>>>This might be crazy to many. 
>>>>
>>>>
>>>>
>>>>I thought to start with PCCOMPOSITE but i do not think it does exactly what I intend. 
>>>>
>>>>
>>>>Any Idea would be appreciated. 
>>>>
>>>>
>>>>
>>>>A beginner!!! 
>>>>Abdul
>>>>
>>>
>>>
>>>-- 
>>>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
>>>
>>>
>
>
> 
>
>
>
>-- 
>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
>
>
>
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