[petsc-users] MatMult with factored matrix

[Daniel L Crumly]

Matt and Barry - thank you for your replies.  While I was hoping to avoid
accessing the matrix directly, I do appreciate the advice.

 

Have Fun

 

Daniel "The Plaid Mentat" Crumly

Daniel.Crumly at colorado.edu

--------

I give you the desert chameleon, whose ability to blend itself into the
background tells you all you need to know about the roots of ecology and the
foundations of a personal identity.

--Book of Diatribes from the Hayt Chronicle

----Herbert, Frank. Children of Dune 28.

 

From: petsc-users-bounces at mcs.anl.gov
[mailto:petsc-users-bounces at mcs.anl.gov] On Behalf Of Barry Smith
Sent: Thursday, July 08, 2010 12:20 PM
To: PETSc users list
Subject: Re: [petsc-users] MatMult with factored matrix

 

 

On Jul 8, 2010, at 10:18 AM, Daniel L Crumly wrote:





Thank you for the  quick reply - I actually do want the action of the
factored matrix (or preconditioner) on a vector.  Is there a recommended
workaround?

 

   If A =approx L*U then applying the preconditioner involves triangular
solves of L and U and use MatSolve() to do this. If you want to actually
apply L*U we don't have code for this, as Matt mentioned. But note that
right, left or split (symmetric) preconditioning do not need the application
of L or U only the triangular solves.

 

   If you want to form the product L*U to see how "far" from A it is we
don't have code for that, you could write a new routine that directly access
the data structure and does the product for you, but since it is not needed
for traditional linear solvers we don't provide such a thing.

 

   Barry

 

 

Thanks

 

Daniel "The Plaid Mentat" Crumly

Daniel.Crumly at colorado.edu

--------

I give you the desert chameleon, whose ability to blend itself into the
background tells you all you need to know about the roots of ecology and the
foundations of a personal identity.

--Book of Diatribes from the Hayt Chronicle

----Herbert, Frank. Children of Dune 28.

 

From: petsc-users-bounces at mcs.anl.gov
[mailto:petsc-users-bounces at mcs.anl.gov] On Behalf Of Matthew Knepley
Sent: Thursday, July 08, 2010 11:10 AM
To: PETSc users list
Subject: Re: [petsc-users] MatMult with factored matrix

 

On Thu, Jul 8, 2010 at 7:06 PM, Daniel L Crumly <daniel.crumly at colorado.edu>
wrote:

Hello all -

Is there a recommended way to multiply a factored matrix by a vector
(effectively MatMult where the matrix is a factored matrix or
preconditioner)?  Specifically, I would like to get take the ILU
factorization of a matrix, then multiply a vector by this approximation.

 

Do you actually want the action, or the action of the inverse? We only
provide

the action of the inverse

 

http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpag
es/Mat/MatSolve.html

 

    Matt

 

What I currently have is:

 ierr = PCGetType(pc, &pctype);CHKERRQ(ierr);
 if (strcmp(pctype, PCILU) == 0 || strcmp(pctype, PCICC) == 0) {
   ierr = PCFactorGetMatrix(pc, &M);CHKERRQ(ierr);
   ierr = MatMult(M, x, Mx);CHKERRQ(ierr);
 }

which throws the runtime error (I'm currently using PETSc 3.0.0-p8.):

[0]PETSC ERROR: --------------------- Error Message
------------------------------------
[0]PETSC ERROR: Object is in wrong state!
[0]PETSC ERROR: Not for factored matrix!
[0]PETSC ERROR:
------------------------------------------------------------------------

Any suggestions are greatly appreciated, thank you.

Daniel "The Plaid Mentat" Crumly
Daniel.Crumly at colorado.edu
--------
I give you the desert chameleon, whose ability to blend itself into the
background tells you all you need to know about the roots of ecology and the
foundations of a personal identity.
--Book of Diatribes from the Hayt Chronicle
----Herbert, Frank. Children of Dune 28.







-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener

 

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