MPI_SCATTER_INIT(3)				     Open MPI				       MPI_SCATTER_INIT(3)

       MPI_Scatter  <#mpi-scatter>,  MPI_Iscatter  <#mpi-iscatter>, MPI_Scatter_init - Sends data from one task to
       all tasks in a group.

SYNTAX
   C Syntax
	  #include <mpi.h>

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

	  int MPI_Iscatter(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
	       void *recvbuf, int recvcount, MPI_Datatype recvtype, int root,
	       MPI_Comm comm, MPI_Request *request)

	  int MPI_Scatter_init(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
	       void *recvbuf, int recvcount, MPI_Datatype recvtype, int root,
	       MPI_Comm comm, MPI_Info info, MPI_Request *request)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_SCATTER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
		       RECVTYPE, ROOT, COMM, IERROR)
	       <type>  SENDBUF(*), RECVBUF(*)
	       INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT
	       INTEGER COMM, IERROR

	  MPI_ISCATTER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
		       RECVTYPE, ROOT, COMM, REQUEST, IERROR)
	       <type>  SENDBUF(*), RECVBUF(*)
	       INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT
	       INTEGER COMM, REQUEST, IERROR

	  MPI_SCATTER_INIT(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
		       RECVTYPE, ROOT, COMM, INFO, REQUEST, IERROR)
	       <type>  SENDBUF(*), RECVBUF(*)
	       INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT
	       INTEGER COMM, INFO, REQUEST, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Scatter(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
		       root, comm, ierror)
	       TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
	       TYPE(*), DIMENSION(..) :: recvbuf
	       INTEGER, INTENT(IN) :: sendcount, recvcount, root
	       TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
	       TYPE(MPI_Comm), INTENT(IN) :: comm
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

	  MPI_Iscatter(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
		       root, comm, request, ierror)
	       TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
	       TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
	       INTEGER, INTENT(IN) :: sendcount, recvcount, root
	       TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
	       TYPE(MPI_Comm), INTENT(IN) :: comm
	       TYPE(MPI_Request), INTENT(OUT) :: request
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

	  MPI_Scatter_init(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
		       root, comm, info, request, ierror)
	       TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
	       TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
	       INTEGER, INTENT(IN) :: sendcount, recvcount, root
	       TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
	       TYPE(MPI_Comm), INTENT(IN) :: comm
	       TYPE(MPI_Info), INTENT(IN) :: info
	       TYPE(MPI_Request), INTENT(OUT) :: request
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • sendbuf: Address of send buffer (choice, significant only at root).

       • sendcount: Number of elements sent to each process (integer, significant only at root).

       • sendtype: Datatype of send buffer elements (handle, significant only at root).

       • recvcount: Number of elements in receive buffer (integer).

       • recvtype: Datatype of receive buffer elements (handle).

       • root: Rank of sending process (integer).

       • comm: Communicator (handle).

       • info: Info (handle, persistent).

OUTPUT PARAMETERS
       • recvbuf: Address of receive buffer (choice).

       • request: Request (handle, non-blocking only).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       MPI_Scatter <#mpi-scatter> is the inverse operation to MPI_Gather <#mpi-gather>.

       The outcome is as if the root executed n send operations,

	  MPI_Send(sendbuf + i * sendcount * extent(sendtype), sendcount,
		   sendtype, i, ...);

       and each process executed a receive,

	  MPI_Recv(recvbuf, recvcount, recvtype, i, ...).;

       An alternative description is that the root sends a message with MPI_Send(sendbuf, sendcount * n, sendtype,
       ...). This message is split into n equal segments, the ith segment is sent to the ith process in the group,
       and each process receives this message as above.

       The send buffer is ignored for all nonroot processes.

       The type signature associated with sendcount, sendtype at the root must be  equal  to  the  type	 signature
       associated  with	 recvcount,  recvtype  at  all	processes (however, the type maps may be different).  This
       implies that the amount of data sent must be equal to the amount of data received,  pairwise  between  each
       process and the root. Distinct type maps between sender and receiver are still allowed.

       All  arguments  to  the	function are significant on process root, while on other processes, only arguments
       recvbuf, recvcount, recvtype, root, comm are significant. The arguments root and comm must  have	 identical
       values on all processes.

       The specification of counts and types should not cause any location on the root to be read more than once.

       Rationale:  Though not needed, the last restriction is imposed so as to achieve symmetry with MPI_Gather <#
       mpi-gather>, where the corresponding restriction (a multiple-write restriction) is necessary.

       Example: The reverse of Example 1 in the MPI_Gather <#mpi-gather> manpage. Scatter sets of  100	ints  from
       the root to each process in the group.

	  MPI_Comm comm;
	  int gsize,*sendbuf;
	  int root, rbuf[100];
	  ...
	  MPI_Comm_size(comm, &gsize);
	  sendbuf = (int *)malloc(gsize*100*sizeof(int));
	  ...
	  MPI_Scatter(sendbuf, 100, MPI_INT, rbuf, 100,
		      MPI_INT, root, comm);

USE OF IN-PLACE OPTION
       When  the  communicator	is  an intracommunicator, you can perform a scatter operation in-place (the output
       buffer is used as the input buffer). Use the variable  MPI_IN_PLACE  as	the  value  of	the  root  process
       recvbuf. In this case, recvcount and recvtype are ignored, and the root process sends no data to itself.

       Note that MPI_IN_PLACE is a special kind of value; it has the same restrictions on its use as MPI_BOTTOM.

       Because	the  in-place option converts the receive buffer into a send-and-receive buffer, a Fortran binding
       that includes INTENT must mark these as INOUT, not OUT.

WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
       When the communicator is an inter-communicator, the root process in the	first  group  sends  data  to  all
       processes  in the second group. The first group defines the root process. That process uses MPI_ROOT as the
       value of its root argument. The remaining processes use MPI_PROC_NULL as the value of their root	 argument.
       All  processes  in  the	second	group use the rank of that root process in the first group as the value of
       their root argument. The receive buffer argument of the root process in the first group must be	consistent
       with the receive buffer argument of the processes in the second group.

ERRORS
       Almost  all MPI routines return an error value; C routines as the return result of the function and Fortran
       routines in the last argument.

       Before the error value is returned, the current MPI error handler associated with the communication  object
       (e.g.,  communicator, window, file) is called.  If no communication object is associated with the MPI call,
       then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler.  When
       MPI_COMM_SELF  is  not  initialized  (i.e., before MPI_Init <#mpi-init>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#mpi-finalize>, or when using the Sessions Model  exclusively)  the	error  raises  the
       initial	error  handler.	 The  initial  error  handler can be changed by calling MPI_Comm_set_errhandler <#
       mpi-comm-set-errhandler> on MPI_COMM_SELF when using the World model,  or  the  mpi_initial_errhandler  CLI
       argument	  to   mpiexec	 or   info  key	 to  MPI_Comm_spawn  <#mpi-comm-spawn>/MPI_Comm_spawn_multiple	<#
       mpi-comm-spawn-multiple>.  If no other appropriate error handler has been set, then  the	 MPI_ERRORS_RETURN
       error  handler  is  called  for	MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or  session.  When
	 called on a communicator, it acts as if MPI_Abort <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#mpi-abort> was called on a communicator containing the group
	 of processes in the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       See also:

	  • MPI_Scatterv <#mpi-scatterv>

	  • MPI_Gather <#mpi-gather>

	  • MPI_Gatherv <#mpi-gatherv>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				       MPI_SCATTER_INIT(3)
