[petsc-users] Petsc+Chombo example

[Mark Adams]

On Wed, Aug 12, 2015 at 10:52 PM, Mani Chandra <mc0710 at gmail.com> wrote:

> Thanks for the information. I'm familiar with SNES+DMDA,
>

DMDA will not work with Chombo.  DMDA only works with uniform grids.  My
two (base) classes do the transformations and linearizations for a 1) level
solve and 2) full AMR solve, to a AIJ matrix.

I don't think you want to look at DMs.

Mark


> just not sure it would work with Chombo. But I'll give it a shot.
>
> Cheers,
> Mani
>
> On Wed, Aug 12, 2015 at 5:56 PM, Mark Adams <mfadams at lbl.gov> wrote:
>
>>
>>
>> On Wed, Aug 12, 2015 at 2:29 PM, Mani Chandra <mc0710 at gmail.com> wrote:
>>
>>> Hi,
>>>
>>>
>>>> Chombo (me) creates an MPIAIJ matrix.  So automatic Jacobian assembly
>>>> should work.
>>>>
>>>> I have put a SNES in a Chombo code, but did not use automatic Jacobian
>>>> assembly.
>>>>
>>>
>>> Do you have an example?
>>>
>>
>> If you want to make a SNES solver then you need an "apply" call back
>> function and a way to map Chombo vectors with PETSc vectors.
>>
>> Chombo has a level solver (classes derived from PetscSolver) and an AMR
>> composite matrix constructor class (classes derived from PetscCompGrid) in
>> lib/src/AMRElliptic.  These two class each create these maps, providing
>> methods to "putChomboInPetsc", and so forth.
>>  lib/src/AMRElliptic/PetscSolverI.H has an apply_mfree() method that is a
>> callback function that you give to PETSc to apply an operator.  There are
>> examples in Chombo on how to use/construct these two classes, or two
>> installations of them.  Each of these classes has a Poisson and a 2D
>> Viscous Tensor instantiation.
>>
>> You probably want to look at PETSc SNES examples if you are not familiar
>> with SNES to get an idea of what you need to provide.  Then, look at the
>> appropriate Chombo class as a place start.  I am guessing that you will
>> want to write your own solver and just use these classes to get these
>> mapping methods.  Wrapping a Chombo operator (apply) and solver in a SNES
>> is not hard and PetscSolverI.H has examples.
>>
>> These codes only have one user each (and they are both ANAG staff
>> members), so they are pretty immature codes.
>>
>> Mark
>>
>>
>>> Thanks,
>>> Mani
>>>
>>
>>
>
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