Can I modify x on SampleShellPCApply callback ? I am running debian (gcc-6.4), using petsc-dev synchronized on: >> git log commit f9d5775f43f69cbce5a7014a6ce3b24cc0e1214a (HEAD -> master, origin/master, origin/HEAD)
when I run petsc/src/ksp/ksp/examples/tutorials/ex15.c, I get: >> mpirun -n 2 ./ex15.exe -user_defined_pc Norm of error 5.90715e-08 iterations 15 OK, so far, so good. Now, I just modify x in SampleShellPCApply (reset to 0. at the end = doing nothing): >> git diff diff --git a/src/ksp/ksp/examples/tutorials/ex15.c b/src/ksp/ksp/examples/tutorials/ex15.c index badccd93b5..482e5ae6b5 100644 --- a/src/ksp/ksp/examples/tutorials/ex15.c +++ b/src/ksp/ksp/examples/tutorials/ex15.c @@ -296,6 +296,7 @@ PetscErrorCode SampleShellPCApply(PC pc,Vec x,Vec y) ierr = PCShellGetContext(pc,(void**)&shell);CHKERRQ(ierr); ierr = VecPointwiseMult(y,x,shell->diag);CHKERRQ(ierr); + ierr = VecSet(x, 0.);CHKERRQ(ierr); return 0; } >> mpirun -n 2 ./ex15.exe -user_defined_pc [0]PETSC ERROR: --------------------- Error Message -------------------------------------------------------------- [0]PETSC ERROR: Object is in wrong state [0]PETSC ERROR: Vec is locked read only, argument # 1 [1]PETSC ERROR: #1 VecSet() line 547 in /home/fghoussen/Documents/INRIA/petsc/src/vec/vec/interface/rvector.c [1]PETSC ERROR: #2 SampleShellPCApply() line 299 in /home/fghoussen/Documents/INRIA/petsc/local/../src/ksp/ksp/examples/tutorials/ex15.c Why is that ? Is there a way to "unlock" x ? It seems, it's possible to modify y but not x: why ? >> git diff diff --git a/src/ksp/ksp/examples/tutorials/ex15.c b/src/ksp/ksp/examples/tutorials/ex15.c index badccd93b5..98ae001319 100644 --- a/src/ksp/ksp/examples/tutorials/ex15.c +++ b/src/ksp/ksp/examples/tutorials/ex15.c @@ -294,6 +294,7 @@ PetscErrorCode SampleShellPCApply(PC pc,Vec x,Vec y) SampleShellPC *shell; PetscErrorCode ierr; + ierr = VecSet(y, 0.);CHKERRQ(ierr); ierr = PCShellGetContext(pc,(void**)&shell);CHKERRQ(ierr); ierr = VecPointwiseMult(y,x,shell->diag);CHKERRQ(ierr); >> mpirun -n 2 ./ex15.exe -user_defined_pc Norm of error 5.90715e-08 iterations 15 Does PETSc uses x even after the callback has been called ? My understanding is that at the end of the callback only y matters: y replaces x that has become no-use (y is the new residu): am I wrong ? If possible, I would like to reuse x (avoiding to re-create a vector) ? Is there a way to "unlock" x ? Franck
