[petsc-users] time stepping questions

[Jed Brown]

Gideon Simpson <gideon.simpson at gmail.com> writes:
>> If you created a viewer, you need to destroy it.
>
> But the destruction of the viewer is handled by the TSMonitor routine, and not done manually, with a PetscViewerDestroy routine?

TS monitoring calls the destroy function that you passed to TSMonitorSet.

> What I find confusing about that, though, is that you call PetscViewerBinaryOpen with &ctx, a pointer to the viewer object, and this makes sense, because the command is:
>
> PetscErrorCode  PetscViewerBinaryOpen(MPI_Comm comm,const char name[],PetscFileMode type,PetscViewer *binv)

You're creating the PetscViewer.  C has pass-by-value semantics, so if
you want to change the handle, you have to &viewer.

> but for TSMonitorSet and TSMonitorSolutionBinary, it’s written as:
> PetscErrorCode  TSMonitorSet(TS ts,PetscErrorCode (*monitor)(TS,PetscInt,PetscReal,Vec,void*),void *mctx,PetscErrorCode (*mdestroy)(void**))
> PetscErrorCode  TSMonitorSolutionBinary(TS ts,PetscInt step,PetscReal ptime,Vec u,void *viewer)
> which makes it look like i should be passing an &ctx, and not the ct. itself.  But this is a minor point.  One works, and one doesn't

The context can be any (pointer) type, so we write void*.  In this case,
it's a

  typedef struct _p_PetscViewer *PetscViewer;

> I was more interested in -ts_monitor.  I suppose I just need to do string processing on that to get the actual times.

Sure, or have your own monitor print whatever information you want.  I
like -ts_adapt_monitor for debugging -- lots more information.
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