[petsc-dev] future pull request about multipreconditioned solvers

[Lawrence Mitchell]

Pierre,

did you attempt to open the pull request in bitbucket.org/petsc/petsc (not allowed unless you have petsc write access), or in your fork (allowed, and you can target at petsc/petsc master)?

Lawrence

> On 11 Jun 2019, at 14:55, Smith, Barry F. via petsc-dev <petsc-dev at mcs.anl.gov> wrote:
> 
> 
>  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
>> 
>