Re: [Libmesh-users] matrix free scheme

[Vijay S. M. <vi...@gm...>]

I've attached the message from Ben Kirk. Also attached is the example
program that he sent out. See below for his original mail.

On a side note, I have written a working code with Matrix-free technique =
to
solve a nonlinear, transient diffusion-reaction problem. It still needs =
few
refinements and I will send it here or maybe upload it somewhere soon =
for
all those interested.

-----Original Message-----
From: Benjamin Kirk [mailto:ben...@na...]=20
Sent: Wednesday, January 23, 2008 9:40 AM
To: Vijay M; lib...@li...
Subject: Re: [Libmesh-users] Support for Matrix-free algorithms

Here is a really, really raw example, the comments are not clear right =
now,
but I wanted to keep you informed.  This requires the latest svn branch =
to
work.

Unpack it in the ./examples directory and run make.

Run it as

$ ./ex19-dbg -snes_view -r 4
for a successive approximation which will converge linearly, and

$ ./ex19-dbg -snes_view -r 4 -snes_mf_operator
for a matrix-free approach in the iterative solver which will converge
quadratically.

> Anyway, I do have a question regarding using PETSc object with =
LibMesh. I
> have been trying to use Petsc objects Mats, Vecs and SNES solver with
> Libmesh but the one thing I cant seem figure out is how to set the
> nonlinear_solver public attribute of say a NonlinearImplicitSystem =
object
to
> a PETSc SNES object which I have created and initialized separately.
Since,
> the SNES object used in the wrapper PetscNonlinearSolver is private, I
don=B9t
> understand how this can be done.
>=20
> Have I missed something and taken a completely wrong path on this ? I
would
> very much appreciate any comments that you can provide to help me out
here.

The user interface is totally up for discussion since I am the only one =
who
as exercised it to date.  (I am sure Roy will have some comments!)  It =
seems
to me the right approach will be to add a method which gives the user =
access
to the SNES object?  From there the KSP, Mat, Vec, PC, etc... can be
accessed.  This would be similar to the approach used in the
PetscLinearSolver.

-Ben


-----Original Message-----
From: li pan [mailto:li...@ya...]=20
Sent: Wednesday, January 30, 2008 3:25 AM
To: lib...@li...
Cc: vi...@gm...
Subject: matrix free scheme

Dear all,
I remember that there was a discussion about matrix
free scheme with libmesh before X'mas. I'd like to ask
if somebody has got a example code for this.

thanx

pan


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