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MPI_Iscan(3)			      MPI			  MPI_Iscan(3)

NAME
       MPI_Iscan  -   Computes the scan	(partial reductions) of	data on	a col-
       lection of processes in a nonblocking way

SYNOPSIS
       int MPI_Iscan(const void	*sendbuf, void *recvbuf, int count,
       MPI_Datatype datatype, MPI_Op op, MPI_Comm comm,
       MPI_Request *request)

       int MPI_Iscan_c(const void *sendbuf, void *recvbuf, MPI_Count count,
       MPI_Datatype datatype, MPI_Op op, MPI_Comm comm,
       MPI_Request *request)

INPUT PARAMETERS
       sendbuf
	      -	starting address of send buffer	(choice)
       count  -	number of elements in input buffer (non-negative integer)
       datatype
	      -	data type of elements of input buffer (handle)
       op     -	operation (handle)
       comm   -	communicator (handle)

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

NOTES ON COLLECTIVE OPERATIONS
       The reduction functions ( MPI_Op	) do not return	an error value.	 As  a
       result,	if  the	 functions  detect an error, all they can do is	either
       call MPI_Abort or silently skip the problem.  Thus, if you  change  the
       error handler from MPI_ERRORS_ARE_FATAL to something else, for example,
       MPI_ERRORS_RETURN , then	no error may be	indicated.

       The  reason  for	 this is the performance problems in ensuring that all
       collective routines return the same error value.

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_ARG
	      -	Invalid	argument.  Some	argument is invalid and	is not identi-
	      fied by a	specific error class (e.g., MPI_ERR_RANK ).
       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_OP
	      -	Invalid	operation.  MPI	operations (objects of type  MPI_Op  )
	      must either be one of the	predefined operations (e.g., MPI_SUM )
	      or created with MPI_Op_create .

       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_Iscan(3)

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