[petsc-users] CG+GAMG convergence issues in GHEP Krylov-Schur for some MPI runs

[Barry Smith]

  I am more optimistic about valgrind than Mark. I first try valgrind and if that fails to be helpful then use the debugger. valgrind has the advantage that it finds the FIRST place that something is wrong, while in the debugger it is kind of late at the crash.

  Valgrind should not be noisy, if it is then the applications/libraries should be cleaned up so that they are valgrind clean and then valgrind is useful.

  Barry



> On Nov 3, 2015, at 7:47 AM, Mark Adams <mfadams at lbl.gov> wrote:
> 
> BTW, I think that our advice for segv is use a debugger.  DDT or Totalview, and gdb if need be, will get you right to the source code and will get 90% of bugs diagnosed.  Valgrind is noisy and cumbersome to use but can diagnose 90% of the other 10%.
> 
> On Tue, Nov 3, 2015 at 7:32 AM, Denis Davydov <davydden at gmail.com> wrote:
> Hi Jose,
> 
> > On 3 Nov 2015, at 12:20, Jose E. Roman <jroman at dsic.upv.es> wrote:
> >
> > I am answering the SLEPc-related questions:
> > - Having different number of iterations when changing the number of processes is normal.
> the change in iterations i mentioned are for different preconditioners, but the same number of MPI processes.
> 
> 
> > - Yes, if you do not destroy the EPS solver, then the preconditioner would be reused.
> >
> > Regarding the segmentation fault, I have no clue. Not sure if this is related to GAMG or not. Maybe running under valgrind could provide more information.
> will try that.
> 
> Denis.
>