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MPI_Neighbor_allgather(3)	      MPI	     MPI_Neighbor_allgather(3)

NAME
       MPI_Neighbor_allgather  -   Gathers data	from all neighboring processes
       and distribute the combined data	to all neighboring processes

SYNOPSIS
       int MPI_Neighbor_allgather(const	void *sendbuf, int sendcount,
       MPI_Datatype sendtype, void *recvbuf, int recvcount,
       MPI_Datatype recvtype, MPI_Comm comm)

       int MPI_Neighbor_allgather_c(const void *sendbuf, MPI_Count sendcount,
       MPI_Datatype sendtype, void *recvbuf,
       MPI_Count recvcount, MPI_Datatype recvtype,
       MPI_Comm	comm)

INPUT PARAMETERS
       sendbuf
	      -	starting address of send buffer	(choice)
       sendcount
	      -	number of elements sent	to each	neighbor  (non-negative	 inte-
	      ger)
       sendtype
	      -	data type of send buffer elements (handle)
       recvcount
	      -	 number	 of elements received from each	neighbor (non-negative
	      integer)
       recvtype
	      -	data type of receive buffer elements (handle)
       comm   -	communicator with topology structure (handle)

OUTPUT PARAMETERS
       recvbuf
	      -	starting address of receive buffer (choice)

NOTES
       In this function, each process i	gathers	data items from	each process j
       if an edge (j,i)	exists in the topology graph, and each process i sends
       the same	data items to all processes j where an edge (i,j) exists.  The
       send  buffer  is	sent to	each neighboring process and the l-th block in
       the receive buffer is received from the l-th neighbor.

THREAD AND INTERRUPT SAFETY
       This routine is thread-safe.  This  means  that	this  routine  may  be
       safely  used by multiple	threads	without	the need for any user-provided
       thread locks.  However, the routine is not interrupt safe.   Typically,
       this  is	due to the use of memory allocation routines such as malloc or
       other non-MPICH runtime routines	that  are  themselves  not  interrupt-
       safe.

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.

ERRORS
       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_Comm_set_errhandler (for com-
       municators), MPI_File_set_errhandler (for files),  and  MPI_Win_set_er-
       rhandler	 (for  RMA windows).  The MPI-1	routine	MPI_Errhandler_set may
       be used but its	use  is	 deprecated.   The  predefined	error  handler
       MPI_ERRORS_RETURN  may  be  used	 to cause error	values to be returned.
       Note that MPI does not guarantee	that an	MPI program can	continue  past
       an  error;  however, MPI	implementations	will attempt to	continue when-
       ever possible.

       MPI_SUCCESS
	      -	No error; MPI routine completed	successfully.
       MPI_ERR_BUFFER
	      -	Invalid	buffer pointer.	 Usually a null	buffer	where  one  is
	      not valid.
       MPI_ERR_COMM
	      -	 Invalid communicator.	A common error is to use a null	commu-
	      nicator in a call	(not even allowed in MPI_Comm_rank ).
       MPI_ERR_COUNT
	      -	Invalid	count argument.	 Count arguments must be non-negative;
	      a	count of zero is often valid.
       MPI_ERR_TYPE
	      -	Invalid	datatype argument.  Additionally, this error can occur
	      if an uncommitted	MPI_Datatype (see MPI_Type_commit ) is used in
	      a	communication call.
       MPI_ERR_OTHER
	      -	Other error; use  MPI_Error_string  to	get  more  information
	      about this error code.

				   2/3/2025	     MPI_Neighbor_allgather(3)

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