petsc-3.7.3 2016-07-24
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# PetscGatherNumberOfMessages

Computes the number of messages a node expects to receive

### Synopsis

    #include "petscsys.h"
    PetscErrorCode  PetscGatherNumberOfMessages(MPI_Comm comm,const PetscMPIInt iflags[],const PetscMPIInt ilengths[],PetscMPIInt *nrecvs)

Collective on MPI_Comm

### Input Parameters

| 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.

### Output Parameters

nrecvs -number of messages received

### Notes

With this info, the correct message lengths can be determined using PetscGatherMessageLengths()

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.

### See Also

PetscGatherMessageLengths()

Level:developer
Location: src/sys/utils/mpimesg.c
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