Re: [petsc-users] Checking for NULL Objects in Fortran

[Fabian Jakub]

Allright,

Many thanks for the super prompt response!





On 10.09.2018 23:30, Smith, Barry F. wrote:

    Sorry for your difficulties

    The recent branch barry/change-fortran-null was intended to simplify the 
handling of NULL slightly in Fortran and make it more consistent with the 
handling in C. It essentially changed  %v to be equal to 0 for NULL objects 
rather than -1. This allows easier passing objects directly to C code also.

     We did not intend to change the user API; we intended that comparisons 
with PETSC_NULL_DM would behave exactly as before.

     Unfortunately it looks like some places in the code had -1 hardwired, for 
example,

/* Definitions of Fortran Wrapper routines */
PETSC_EXTERN void PETSC_STDCALL dmplexdistribute_(DM *dm, PetscInt *overlap, 
PetscSF *sf, DM *dmParallel, int *ierr)
{
   CHKFORTRANNULLOBJECT(sf);
   CHKFORTRANNULLOBJECT(dmParallel);
   *ierr = DMPlexDistribute(*dm, *overlap, sf, dmParallel);
   if (dmParallel && !*dmParallel) *dmParallel = (DM)-1;
}

I did not know about this hardwiring and thus did not update them while making 
the new branch.

The branch barry/change-fortran-null-fixup fixes the two bad uses of -1 that 
you pointed out. Please try it and let us know other problems that come up 
since we are planning a release very shortly.

On Sep 10, 2018, at 4:02 PM, Fabian.Jakub <fabian.ja...@physik.uni-muenchen.de> 
wrote:

Greetings my dear PETSc list.

In my Fortran Code, I usually checked against PETSC_NULL_DM or
PETSC_NULL_IS after calling methods such as DMPlexDistribute or
DMGetStratumIS.

Recently this fails me.

I saw the DMPlexDistribute example in
dm/label/examples/tutorials/ex1f90.F90

where the value of dm_distributed%v is compared against -1

     We do not recommend the usage of dm_distributed%v /= 0 and instead 
recommend comparing with the appropriate PETSC_NULL_XXX as you have done. (the 
%v business will work, we just don't recommend it).

Now, after the recent change of PETSC_NULL_DM (tDM(1) -> tDM(0) in
3d1df95b1) I am not 100% percent sure how to deal with it.

Could you please clarify if testing against ``-1`` is the intended way
to do it or may this change again soonish?

     Definitely not. Your code should remain the same and we simply need to fix 
the stray -1 to change them to 0.

    Barry

Many Thanks,

Fabian


Here some code snippets to clarify what lead me to put up this question...

This used to validate:

call DMGetStratumIS(dm, 'DomainBoundary', SIDEFACE, bc_idx, ierr)
if (bc_ids.eq.PETSC_NULL_IS) then ! dont have domain boundary points
...
endif

or

call DMPlexDistribute(dm, i0, PETSC_NULL_SF, dmdist, ierr)
if (dmdist.eq.PETSC_NULL_DM) then ! DM was not distributed
endif


Now I could do something like:

if(bc_ids%v.eq.-1)

of (dmdist%v.eq.-1)

...