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/manualpages/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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20100708/2407833c/attachment-0001.htm>
