[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.Jakub at 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)
>>
>> ...
>>