Gathers together values from a group of processes


#include "mpi.h"
int MPI_Gather ( void *sendbuf, int sendcnt, MPI_Datatype sendtype, 
                void *recvbuf, int recvcount, MPI_Datatype recvtype, 
                int root, MPI_Comm comm )

Input Parameters

sendbuf starting address of send buffer (choice)
sendcount number of elements in send buffer (integer)
sendtype data type of send buffer elements (handle)
recvcount number of elements for any single receive (integer, significant only at root)
recvtype data type of recv buffer elements (significant only at root) (handle)
root rank of receiving process (integer)
comm communicator (handle)

Output Parameter

address of receive buffer (choice, significant only at root)

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

No error; MPI routine completed successfully.
Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
Invalid buffer pointer. Usually a null buffer where one is not valid.