#include "petscsys.h" PetscErrorCode PetscGatherNumberOfMessages(MPI_Comm comm,const PetscMPIInt iflags[],const PetscMPIInt ilengths[],PetscMPIInt *nrecvs)Collective on MPI_Comm
| comm | - Communicator | |
| iflags | - an array of integers of length sizeof(comm). A '1' in ilengths[i] represent a message from current node to ith node. Optionally NULL | |
| ilengths | - Non zero ilengths[i] represent a message to i of length ilengths[i]. Optionally NULL. |
Either iflags or ilengths should be provided. If iflags is not provided (NULL) it can be computed from ilengths. If iflags is provided, ilengths is not required.