> On Mar 31, 2015, at 9:03 PM, Juris Vencels <[email protected]> wrote: > > Hello PETSc Users, > > I am using Matrix-Free SNES solver with the following options > PETSC_OPTIONS="ksp_type gmres -snes_monitor_short -snes_mf -user_precond" > > and shell-ILU preconditioner that I create as following: > > ! =============================== > > call PCSetType(pc,PCSHELL,ierr) > call PCShellSetUp > call PCShellSetApply(pc,PCShellApply,ierr) > call PCShellSetName(pc,"ShellPC",ierr) > > ! =============================== > > subroutine PCShellSetUp() > implicit none > > call SetInitialMatrix ! Assambles matrix A > > call PCCreate(PETSC_COMM_WORLD,mf_prec,ierr) > call PCSetType(mf_prec,PCILU,ierr) > call PCSetOperators(mf_prec,A,A,ierr) > call PCSetUp(mf_prec,ierr) > call PCShellSetName(mf_prec,"LinPC",ierr) > > end subroutine PCShellSetUp > > ! =============================== > > subroutine PCShellApply(pc_tmp,x_tmp,y_tmp,ierr) > implicit none > PC :: pc_tmp > Vec :: x_tmp,y_tmp > PetscErrorCode :: ierr > > call PCApply(mf_prec,x_tmp,y_tmp,ierr) > > end subroutine PCShellApply > > ! =============================== > > * If matrix A changes during a simulation, how can I update preconditioner? > Is calling "PCSetUp(mf_prec,ierr)" enough?
No, the model is that each time the matrix changes the PCSetUp is called automatically and so is a shell set up if you have provided it, so you need to change your PCShellSetUp() function so that it can be called repeatedly for each new matrix and call > call PCShellSetApply(pc,PCShellSetUp,ierr) when you create the Shell PC. Then make a test run in the debugger to make sure that your setup is being called each time the matrix changes. > > * Function PCView prints out information about type and size of > preconditioner. Can I view/get preconditioner matrix itself? I want to > compare it with reference matrix. > > If I try to MatView factored matrix: > call PCFactorGetMatrix(mf_prec,pcmat,ierr) > call MatView(pcmat, PETSC_VIEWER_STDOUT_SELF,ierr) > > Then I get the following error: > [0]PETSC ERROR: No viewers for factored matrix except ASCII info or > info_detailed The LU factors of sparse matrices are rather complicated beasts, there is no reasonable way to see their numerical values and related them to original matrix. A note about terminology: We refer to the "preconditioner matrix" sometimes, it means "the matrix FROM WHICH a preconditioner is built." With ILU the "preconditioner matrix" is factored into L and U (which is what PCFactorGetMatrix() returns. The L and U are the resulting preconditioner, they are not the "matrix from which the preconditioner is built." Note: also if you are using ILU preconditioning, you do not need to use PCSHELL, you can just use PCSetType(pc,PCILU) or -pc_type ilu. Barry > > Thanks! > > >
