On , 2020Mar17, at 13:15, Mark Adams <[email protected]<mailto:[email protected]>> wrote: Is the PETSc model that you don't inialized PETSc object to NULL because you check that pointers are valid PETSc pointers instead of testing on NULL? I think petsc has switched to the mpi/f08 model where objects are no longer opaque pointers hiding in INTEGERs, but actual Fortran derived Type objects. At least in MPI these days MPI_COMM_NULL is not a constant but a Type(MPI_Comm) variable. Victor.