[CIG-CS] Discontinuous viscosity

[Walter Landry]

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Matthew Knepley <knepley at mcs.anl.gov> wrote:
> On Mon, Mar 5, 2012 at 9:01 AM, Walter Landry <walter at geodynamics.org>wrote:
> 
>> Back to the list.
>>
>> Matthew Knepley <knepley at mcs.anl.gov> wrote:
>> > 2012/3/4 Walter Landry <walter at geodynamics.org>
>> > 2) You should be using PETSc, because even with GS, you could
>> >     converge in 1000 iterations by partitioning fields using
>> >     PCFIELDSPLIT. You could do it in < 10 using a nice Schur
>> >     complement preconditioner.
>>
>> Not yet.  The point of this exercise is to have a method that I can
>> eventually plug into Gamr.  Gamr uses SAMRAI, so I would only be able
>> to use Petsc for the solve on the coarsest level.  I still need a
>> smoother for the finer levels.
> 
> I though SAMRAI could use PETSc on all levels. If not, the design is quite
> crappy. Have you talked to Michael Pernice abut this?

I take it back.  Samrai defines a custom vector class that can be used
as a drop-in replacement for Petsc's Vec.  It does not implement all
of operations defined in Petsc's VecOps.  In particular, these are not
implemented and will abort at runtime

  vecSetValues
  vecAssemblyBegin
  vecAssemblyEnd
  vecSetOption
  vecSetValuesBlocked
  vecPlaceArray
  vecReplaceArray
  vecReciprocal
  vecViewNative
  vecConjugate
  vecSetLocalToGlobalMapping
  vecSetValuesLocal
  vecResetArray
  vecSetFromOptions
  vecLoad
  vecPointwiseMax
  vecPointwiseMaxAbs
  vecPointwiseMin
  vecGetValues

these give bogus results for the index (though the main result is ok)

  vecMax
  vecMin

and these always return zero

  getDataSize
  getLocalDataSize

So I do not know which solvers will work and which will not.

There is also an interface that lets you use Petsc's SNES as a driver
for the overall solution.  That, I believe, works.  I had to patch
Samrai to build with Petsc 3.1.0, and I used their example as a test.
I sent a patch to the SAMRAI developers and got no response.

With that said, I am still at the point where I am trying to figure
out what works.  It is quite possible that I will use SNES in the
final code.

Cheers,
Walter Landry