PetscSplitOwnership

Given a global (or local) length determines a local (or global) length via a simple formula

#include "petsc.h" 
int PetscSplitOwnership(MPI_Comm comm,int *n,int *N)

Collective on MPI_Comm (if N is PETSC_DECIDE)

	comm	- MPI communicator that shares the object being divided
	n	- local length (or PETSC_DECIDE to have it set)
	N	- global length (or PETSC_DECIDE)

n and N cannot be both PETSC_DECIDE

If one processor calls this with N of PETSC_DECIDE then all processors must, otherwise the program will hang.