[petsc-users] PCDiagonalScale

[Klaij, Christiaan]

Barry,

I do not want to use it for the reason given in the manual.

Instead I'm trying to use SIMPLE as a preconditioner for a colocated, cell-centered FV discretization of the incompressible Navier-Stokes equations. I'm using a matfree approach for the matrix and the (right) preconditioner. I would like to scale the system as D A M D^{-1} z = D b but I get the feeling that PCDiagonalScaleSet with GCR doesn't do anything.

How about Jed's comment:

"GCR also tolerates a variable preconditioner and it does not have such a check. I don't know if that means it can use diagonal scaling or just that someone forgot to check, but you could try it."

Is it just that the check is missing for GCR so that it doesn't apply diagonal scaling and doesn't tell me?

Chris


Message: 3
Date: Thu, 24 Feb 2011 08:08:42 -0600
From: Barry Smith <bsmith at mcs.anl.gov>
Subject: Re: [petsc-users] PCDiagonalScale
To: PETSc users list <petsc-users at mcs.anl.gov>
Message-ID: <699188CA-750D-446A-AD58-C62CB2A75CE2 at mcs.anl.gov>
Content-Type: text/plain; charset=us-ascii


On Feb 23, 2011, at 9:45 AM, Klaij, Christiaan wrote:

> I'm trying to understand the use of PCDiagonalScale since I want to apply additional diagonal scaling when solving my linear system.

   Do you want to use it exactly for the reason given in
   PCSetDiagonalScale - Indicates the left scaling to use to apply an additional left and right
      scaling as needed by certain time-stepping codes.

   Logically Collective on PC

   Input Parameters:
+  pc - the preconditioner context
-  s - scaling vector

   Level: intermediate

   Notes: The system solved via the Krylov method is
$           D M A D^{-1} y = D M b  for left preconditioning or
$           D A M D^{-1} z = D b for right preconditioning


dr. ir. Christiaan Klaij
CFD Researcher
Research & Development
E mailto:C.Klaij at marin.nl
T +31 317 49 33 44

MARIN
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