Macro to be called when an error has been detected,
comm - An MPI communicator, use
PETSC_COMM_SELFunless you know all ranks of another communicator will detect the error
ierr - nonzero error code, see the list of standard error codes in include/petscerror.h
message - error message
This is rarely needed, one should use
PetscCall() and friends to automatically handle error conditions.
Once the error handler is called the calling function is then returned from with the given error code.
Experienced users can set the error handler with