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MPI_Allgather(3)		      MPI		      MPI_Allgather(3)

NAME
       MPI_Allgather  -	  Gathers  data	from all tasks and distribute the com-
       bined data to all tasks

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

       int MPI_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 in send buffer (non-negative	integer)
       sendtype
	      -	data type of send buffer elements (handle)
       recvcount
	      -	number of elements received from any process (non-negative in-
	      teger)
       recvtype
	      -	data type of receive buffer elements (handle)
       comm   -	communicator (handle)

OUTPUT PARAMETERS
       recvbuf
	      -	address	of receive buffer (choice)

NOTES
       The MPI standard	(1.0 and 1.1) says that

       The jth block of	data sent from	each  process  is  received  by	 every
       process and placed in the jth block of the buffer recvbuf .

       This is misleading; a better description	is

       The  block  of  data  sent  from	 the  jth process is received by every
       process and placed in the jth block of the buffer recvbuf .

       This text was suggested by Rajeev Thakur	and  has  been	adopted	 as  a
       clarification by	the MPI	Forum.

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_Allgather(3)

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