I have no first derivatives. In any case, I will now revisit the systems matrix and RHS functions.
________________________________________ From: Barry Smith [[email protected]] Sent: 21 April 2015 19:41 To: Sanjay Kharche Cc: Matthew Knepley; [email protected] Subject: Re: [petsc-users] preconditioning Hmm, zeros on the diagonal that usually indicates either a bug in your code or a "Stokes-like" problem; for Stokes-like problems we recommend using PCFIELDSPLIT, this requires your understanding of the "block structure" of your matrix. Barry > On Apr 21, 2015, at 1:35 PM, Sanjay Kharche <[email protected]> > wrote: > > > Hi > > I just tried Matt's suggestion and tried to guess other preconditioning > options as well. I didnt have the time to think about their appropriateness. > > All preconditioners worked with the actual ts/ex15. gmag took 13 times longer > to finish than the case when I ran without any preconditioner. The fastest > was the jacobi, followed by sor and bjacobi options to -pc_type I could not > guess the names of the other listed preconditioners associated with ts and > snes. > > In my code however, I found that sor and gamg did not work. I got error > messages, and the first few lines are pasted below. My test was on 1 proc and > 4 procs, both giving similar errors with differnent line numbers. The petsc > part of my code is virtually identical to the example. Any comments on what > is missing or can be changed? > > cheers > Sanjay > > > > > [1]PETSC ERROR: --------------------- Error Message > -------------------------------------------------------------- > [1]PETSC ERROR: Arguments are incompatible > [1]PETSC ERROR: Zero diagonal on row 39 > [1]PETSC ERROR: Petsc Release Version 3.5.2, unknown > [1]PETSC ERROR: ./sk2d on a linux-gnu-c-debug named atriumpc.ex.ac.uk by > sanjay Tue Apr 21 19:28:53 2015 > [1]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++ > --with-fc=gfortran --download-fblaslapack --download-mpich > --download-sundials --download-scalapack --with-c2html=0 > [1]PETSC ERROR: #1 MatInvertDiagonal_SeqAIJ() line 1724 in > /media/6c6201d2-4e2e-4b24-8d04-263b5bc06dfa/sanjay/petsc/src/mat/impls/aij/seq/aij.c > [1]PETSC ERROR: #2 MatSOR_SeqAIJ() line 1756 in > /media/6c6201d2-4e2e-4b24-8d04-263b5bc06dfa/sanjay/petsc/src/mat/impls/aij/seq/aij.c > [1]PETSC ERROR: #3 MatSOR_MPIAIJ() line 1483 in > /media/6c6201d2-4e2e-4b24-8d04-263b5bc06dfa/sanjay/petsc/src/mat/impls/aij/mpi/mpiaij.c > [1]PETSC ERROR: #4 MatSOR() line 3643 in > /media/6c6201d2-4e2e-4b24-8d04-263b5bc06dfa/sanjay/petsc/src/mat/interface/matrix.c > [1]PETSC ERROR: #5 PCApply_SOR() line 35 in > /media/6c6201d2-4e2e-4b24-8d04-263b5bc06dfa/sanjay/petsc/src/ksp/pc/impls/sor/sor.c > [1]PETSC ERROR: #6 PCApply() line 440 in > /media/6c6201d2-4e2e-4b24-8d04-263b5bc06dfa/sanjay/petsc/src/ksp/pc/interface/precon.c > > > > From: Matthew Knepley [[email protected]] > Sent: 21 April 2015 16:51 > To: Sanjay Kharche > Cc: [email protected] > Subject: Re: [petsc-users] preconditioning > > On Tue, Apr 21, 2015 at 10:49 AM, Sanjay Kharche > <[email protected]> wrote: > > Hi > > I am working through the KSP examples, but I will ask for any comments in the > mean time. > > I have a TS code for 2D/3D heat equation, starting from ts/ex15. How can I > easily modify this code to include a parallel preconditioner. As of now, I > just need to add a preconditioner which is easy to program. The coefficients > in my systems matrix are constant, but RHS changes at each iteration. > > Use -pc_type gamg. You have the Laplacian + Identity, so this should work > fine. > > Thanks, > > Matt > > cheers > Sanjay > > > > -- > 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
