[petsc-dev] future pull request about multipreconditioned solvers

[Smith, Barry F.]

  Hmm, I can't explain this. Just a guess did you make a new branch with its own name or just work in master? I don't think it should matter but could you try making a branch not called master if yours is called master.


> On Jun 11, 2019, at 7:39 AM, Pierre Gosselet <gosselet at lmt.ens-cachan.fr> wrote:
> 
> Dear Barry, 
> I have done all the steps described in 
> https://bitbucket.org/petsc/petsc/wiki/pull-request-instructions-git
> unfortunately, when I click on "create pull request",
> I get a "access denied" page.
> 
> My branch gosselet/multiprecond can be found here: 
> https://bitbucket.org/pierre_gosselet/petscfork/src/master/
> 
> Best regards
> pierre
> 
> Le vendredi 07 juin 2019 à 17:58 +0000, Smith, Barry F. a écrit :
>>  Pierre,
>> 
>>   Thanks for your generous offer. Maybe you could point us to a
>> repository with the branch with your additions so we could take a
>> look at it and see how it could be adopted into PETSc?
>> 
>>   Barry
>> 
>> 
>>> On Jun 7, 2019, at 11:07 AM, Pierre Gosselet via petsc-dev <
>>> petsc-dev at mcs.anl.gov> wrote:
>>> 
>>> Dear Petsc developers,
>>> 
>>> I am Pierre Gosselet, researcher in computational mechanics from
>>> France
>>> (ENS Paris Saclay / Univ. Lille). Lately I have been working on
>>> multipreconditioned solvers arising from domain decomposition (DD).
>>> I have co-authored some papers with Nicole Spillane whom you
>>> probably know.
>>> 
>>> Together with Nicolas Tardieu from EDF we have done some
>>> developments
>>> in PetSc and we would be happy to share them. Nicolas told me I had
>>> better send you a short notice before making a pull request.
>>> 
>>> We have implemented a MultiPreconditioned Conjugate Gradients
>>> solver
>>> for the SPD case and a MultiPreconditioned Orthomin solver for
>>> general
>>> matrices.
>>> 
>>> These solvers rely on a method with signature 
>>> PCApplyMultiPrecond(PC, Vec in, Mat out) 
>>> We proposed an implementation of this method in the (Restrictive)
>>> Additive Schwarz (R)ASM framework: PCApplyMultiPrecond_ASM(...). 
>>> When preconditioning, each subdomain provides a column which is
>>> used to
>>> expand the search space. There is an experimental use of the
>>> information in NearNullSpace in order to speed up the convergence
>>> (ersatz of Nicholaides' two-level (R)ASM).
>>> 
>>> In practice, there are new files for the solvers (mpcg.c and
>>> mpomin.c),
>>> some features were added in asm.c, and there are few lines added
>>> in  other files in order to declare the solvers. We tried to make a
>>> nice implementation and integration, but we would be happy to have
>>> our
>>> code reviewed for better performance. 
>>> 
>>> 
>>> Unfortunately, from the very limited numerical experiments that we
>>> have
>>> conducted, we do not have tremendous examples to show, the extra
>>> costs
>>> associated with multipreconditioning are not always compensated by
>>> the
>>> improved convergence. In fact, it appears that multipreconditioned
>>> solvers do not behave as well in the (R)ASM framework as in other
>>> DD
>>> frameworks, like FETI(DP) or BDD(C), where the spectrum has a more
>>> favorable shape and where adaptive strategies are available.
>>> 
>>> Anyhow our developments offer opportunities to test mpcg and
>>> mpomin, to
>>> implement new multipreconditioned solvers and new
>>> multipreconditioning
>>> frameworks (one just need to implement PCApplyMultiPrecond_???).
>>> 
>>> I hope you will be interested by these developments,
>>> best regards
>>> pierre
>>> 
>>> 
>>> -- 
>>> Pierre Gosselet
>>> CR CNRS (research agent) 
>>> LMT -- ENS Paris-Saclay/UMR8535
>>> 61 av. du président Wilson, 94235 CACHAN
>>> tel: +33 1 47405333
>>> 
> -- 
> Pierre Gosselet
> CR CNRS (research agent) 
> LMT -- ENS Paris-Saclay/UMR8535
> 61 av. du président Wilson, 94235 CACHAN
> tel: +33 1 47405333
>