Yes, they are automatically initialized to something ((void*)-2 actually). They are NOT automatically initialized to PETSC_NULL_XXX
#define PetscObjectIsNull(obj) (obj%v == 0 .or. obj%v == -2 .or. obj%v == -3) PETSc Fortran has multiple representations of NULL objects. When you want to pass in the meaning "I am a null" you pass PETSC_NULL_XXX. Not the other representations. Barry Why? Well, if variables were initialized to 0 and then got passed into a routine, the routine would see the 0 and think: Oh, the person does not want to set this variable (because passing x would be the same as passing PETSC_NULL_XXX). > On Jul 4, 2025, at 9:59 PM, Randall Mackie <rlmackie...@gmail.com> wrote: > > Thanks Barry > > We were confused because the online manual says: > > PETSc objects are always automatically initialized when declared so you do > not need to (and should not) do > > type(tXXX) x = PETSC_NULL_XXX > XXX x = PETSC_NULL_XXX > > Randy > > >> On Jul 4, 2025, at 6:56 PM, Barry Smith <bsm...@petsc.dev> wrote: >> >> >> You need to pass PETSC_NULL_MAT in those locations, you cannot just pass >> a Mat that has never been created (that is a different kind of NULL matrix >> :-). I have added clearer error checking in >> https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/merge_requests/8526__;!!G_uCfscf7eWS!fCKFD2GQuhS7Ph3ZA3-seSvOMjhBw12nu4QDGsY2xv5BW8-DUzkyLgU0UhWOJsx21qVDDjkua97Nfr43MUTuUsk$ >> >> >> Barry >> >> >>> On Jul 4, 2025, at 10:32 AM, Randall Mackie <rlmackie...@gmail.com> wrote: >>> >>> In the process of upgrading our code to version 3.23, we have run into >>> another issue, this time with nest matrices. >>> >>> In previous versions (well to at least 3.21) it was perfectly fine to pass >>> in null matrix blocks to create a nest matrix. There are situations where >>> we have, for example, only diagonal blocks. That should be allowed and was >>> and worked fine. >>> >>> In petsc 3.23, that no longer is true, or perhaps we do not know what is >>> the proper way to pass in a null matrix. >>> >>> The attached example reproduces this with the following error: >>> >>> [0]PETSC ERROR: Configure options: --force --with-clean=1 >>> --with-scalar-type=complex --with-debugging=1 --with-fortran=1 >>> --download-mpich=1 --with-cxx=0 >>> [0]PETSC ERROR: #1 PetscObjectReference() at >>> /home/rmackie/PETSc/petsc/src/sys/objects/inherit.c:620 >>> [0]PETSC ERROR: #2 MatNestSetSubMats_Nest() at >>> /home/rmackie/PETSc/petsc/src/mat/impls/nest/matnest.c:1407 >>> [0]PETSC ERROR: #3 MatNestSetSubMats() at >>> /home/rmackie/PETSc/petsc/src/mat/impls/nest/matnest.c:1518 >>> [0]PETSC ERROR: #4 MatCreateNest() at >>> /home/rmackie/PETSc/petsc/src/mat/impls/nest/matnest.c:1800 >>> [0]PETSC ERROR: #5 matnest_bug_reproducer.F90:48 >>> >>> >>> Thanks for helping with this, and thanks for all the work on the Fortran >>> interfaces - I’ve been playing around with your new branch and am excited >>> by all the work! >>> >>> Randy >>> <matnest_bug_reproducer.F90> >> >
