[petsc-users] Adapting MatMult and PCMG functions in matrix-free method.

[domenico lahaye]

Hi Jed, 

  Thank you for your reply. The Algorithm II is described in the paper 

@ARTICLE{yoginabben1,
  author = {Erlangga, Y.A. and R. Nabben},
  title = {On a multilevel {K}rylov Method for the {H}elmholtz Equation preconditioned
by Shifted {L}aplacian},
  journal = {Electronic Transaction on Num. Analysis (ETNA)},
  year = {2008},
  volume = {31},
  pages = {403--424},
 }

  Kind wishes, Domenico.


________________________________
 From: Jed Brown <jedbrown at mcs.anl.gov>
To: domenico lahaye <domenico_lahaye at yahoo.com>; PETSc users list <petsc-users at mcs.anl.gov> 
Cc: Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk> 
Sent: Thursday, July 5, 2012 7:47 PM
Subject: Re: [petsc-users] Adapting MatMult and PCMG functions in matrix-free method.
 

Can you reference a paper or some notes on the algorithm?


On Thu, Jul 5, 2012 at 8:40 AM, domenico lahaye <domenico_lahaye at yahoo.com> wrote:

Dear PETSc developers, 
>
>  Thank you for your support to Abdul. 
>
>
>
>   We are in the process of developing a multilevel 
>
>Krylov solver for the Helmholtz equation. Abdul 
>
>has implemented Algorithm I for this purpose. 
>
>We next would like to implement Algorithm II. 
>
>Algorithm || amounts to replacing every occurrence 
>
>of the system matrix $A$ in Algorithm I by 
>
>$M^{-1} A$. This replacement should occur on all 
>
>levels. We thought of two ways to realize this 
>
>replacement. 
>
>
>
>1) We thought of adopting a matrix-free approach, 
>
>and to plug in the operation with  $M^{-1}$ there. 
>
>This would require a ksp context inside MatMult.    
>
>We wonder whether this a approach is feasible to 
>
>take. 
>
>
>
>2) The other approach would by to implement a 
>
>customized pcmg preconditioner that we can adapt 
>
>to our needs. This could be a more elegant approach, 
>
>at the cost of doing more work. Is the assumption 
>
>that the second approach is more elegant correct 
>
>and would you be able to give advice on how to tackle 
>
>this approach? 
>
>
>
>  Kind wishes, Domenico. 
>
>
>
>
>
>
>________________________________
>
>
>
>
>
>----- Forwarded Message -----
>>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: Thursday, 5 July 2012, 15:45
>>Subject: Re: [petsc-users] Adapting MatMult and PCMG functions in matrix-free method.
>> 
>>
>>On Thu, Jul 5, 2012 at 7:34 AM, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk> wrote:
>>
>>Dear developers and users,
>>>Summer greetings.
>>>We have few question listen below: 
>>>
>>>
>>>1. 
>>>
>>>The first question is about adapting " MatMult " function in matrix-free method.
>>>We intend to incorporate a KSP context inside "MatMult" . The immediate question is how to
>>>provide more than one matrices as input. 
>>
>>
>>You provide extra data through the context for the MATSHELL
>> 
>>Is this idea of incorporating a KSP context inside "MatMult" function workable ? Does it make any confrontation 
>>>
>>>with philosophy of development of Petsc. ? 
>>
>>
>>I am not sure you want this. Do you think PCKSP can do what you want? There is not enough information here to help us answer.
>> 
>>2. 
>>>
>>>An other advance level feedback is needed. 
>>>
>>> Re-implementing PCMG function {mg.c } will lead any violation of philosophy of Petsc-development ??
>>
>>
>>Again, there is not enough information. Can you do what you want by just replacing the monitors?
>>
>>
>>  Thanks,
>>
>>
>>     Matt
>> 
>>3. 
>>>
>>>Which one of the above both is more elegant and feasible to work on ? 
>>>
>>>
>>>
>>>
>>>
>>>Thanking in anticipation, 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
>>
>>
>>
>
>
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