Subject: Re: [FFC-dev] Stokes flow problem

From: Brandon Chabaud <[email-masked]>
Date: Fri, 5 Jun 2009 18:00:36 -0500

Is there some way to inform the Krylov solver that constant pressure is in
the null space of the operator from Dolfin?  The only options that I could
find for the KrylovSolver command were setting the solver type and setting
the preconditioner type.

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From: Anders Logg <[email-masked]>
Date: Sat, 6 Jun 2009 12:59:25 +0200

On Fri, Jun 05, 2009 at 06:00:36PM -0500, Brandon Chabaud wrote:
> Is there some way to inform the Krylov solver that constant pressure is in the
> null space of the operator from Dolfin?  The only options that I could find for
> the KrylovSolver command were setting the solver type and setting the
> preconditioner type.

No, that's not included in the interface. You will have to extract the
PETSc Mat pointer using mat() from PETScMatrix and use PETSc calls.

-- 
Anders

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From: Jed Brown <[email-masked]>
Date: Mon, 08 Jun 2009 12:52:41 +0200

> PETSc Mat pointer using mat() from PETScMatrix and use PETSc calls.

Almost.  You need to get the KSP object from the solver and call
KSPSetNullSpace().

Jed

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From: Anders Logg <[email-masked]>
Date: Mon, 8 Jun 2009 13:00:40 +0200

> Almost.  You need to get the KSP object from the solver and call

It looks like the KSP object is not available in the PETScKrylovSolver
interface anymore. Why has it been removed. Garth?

-- 
Anders

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From: "Garth N. Wells" <[email-masked]>
Date: Mon, 08 Jun 2009 17:09:55 +0100

> interface anymore. Why has it been removed. Garth?

Not sure that we ever had it. Anyway, I've added it now. 
PETScKrylovSolver may however need some work to make sure that user 
options are not overridden.

Garth

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