[petsc-users] petsc4py KSP Question

[Gaetan Kenway]

Thanks. I have both the SNES and the linear KSP solver working the way I
want.

One more question: At the beginning of my non-linear SNES function I have
something like

   def formFunction(self, snes, X, F):

        states = X.getArray()

and a X.resetArray() at the end. Am I correct to assume that this is an
efficient pointer assignment to the numpy array and does not involve a
memory copy?

Thanks

Gaetan



On Wed, Mar 7, 2012 at 3:16 AM, Lisandro Dalcin <dalcinl at gmail.com> wrote:

> On 7 March 2012 02:22, Gaetan Kenway <kenway at utias.utoronto.ca> wrote:
> > Hello
> >
> > I'm in the process of using petsc4py to solve a large multidisciplinary,
> > non-linear system and its adjoint. I have the non-linear solution with
> > snes() working correctly and I'm now doing the linear solution.
> >
> > For the non-linear solve, I create the snes and set my user context as
> > follows:
> >    # Create SNES Object
> >   ASContext = ASNKSolver(self) # Context to hold data
> >   snes = PETSc.SNES().createPython(ASContext, comm=self.gcomm)
> >   snes.setFunction(ASContext.formFunction, resVec)
> >
> > For the linear part, I'm a little confused. I currently have
> >
> >     # Create Python Context and KSP Object
> >     KSPContext = AdjointKSPSolver(self) # Context to hold data
> >     ksp = PETSc.KSP().createPython(KSPContext, comm=self.gcomm)
> >
> > What I'm not sure of is how to specify the operator for the KSP solver in
> > the KSPContext object. Is this possible? Is there something like def
> apply()
> > you must do?
> >
> > The petsc4py poisson2d.py example, first creates a Mat, then sets a
> context
> > for that, and then uses ksp.setOperators() to use that matrix. Is this
> the
> > only way to do it? If, so, what is the use of
> > the  PETSc.KSP().createPython() command?
> >
>
> Unless you want to implement a custom KSP/SNES in Python, you should
> just use KSP/SNES.create(). KSP/SNES.createPython() is a rather
> advanced feature, it is not obvious at all how to use them, there are
> no demos nor documentation about it (however, there is some code in
> test/test_{ksp|snes}_py.py ).
>
> Please take a look at the demo/bratu2d and demo/bratu3d about how to
> setup a SNES solver. For KSP, take a look at
> demo/kspsolve/petsc-mat.py and demo/kspsolve/petsc-ksp.py
>
>
>
> --
> Lisandro Dalcin
> ---------------
> CIMEC (INTEC/CONICET-UNL)
> Predio CONICET-Santa Fe
> Colectora RN 168 Km 472, Paraje El Pozo
> 3000 Santa Fe, Argentina
> Tel: +54-342-4511594 (ext 1011)
> Tel/Fax: +54-342-4511169
>
>
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