On Sun, Jul 16, 2017 at 9:07 AM, Franck Houssen <[email protected]> wrote:
> OK, so I need to create a new x. Thanks for the quick answer. > Why would you create a new x. There is some misunderstanding about this routine. You should never need to create a "new x". Matt > Franck > > > ------------------------------ > > *De: *"Matthew Knepley" <[email protected]> > *À: *"Franck Houssen" <[email protected]> > *Cc: *"petsc-dev" <[email protected]> > *Envoyé: *Dimanche 16 Juillet 2017 15:59:09 > *Objet: *Re: [petsc-dev] Can I modify x on SampleShellPCApply callback ? > > On Sun, Jul 16, 2017 at 8:51 AM, Franck Houssen <[email protected]> > wrote: > >> 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 ? >> > > x is the input and should be read-only. Changes cannot have any > mathematical significance because you cannot know > where the x vector would be used subsequently anyway. > > Matt > > Matt > > >> >> 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 >> >> >> > > > -- > 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 > > http://www.caam.rice.edu/~mk51/ > > > -- 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 http://www.caam.rice.edu/~mk51/
