MPI_SCATTERV_INIT(3)				     Open MPI				      MPI_SCATTERV_INIT(3)

       MPI_Scatterv  <#mpi-scatterv>,  MPI_Iscatterv  <#mpi-iscatterv>,	 MPI_Scatterv_init  - Scatters a buffer in
       parts to all tasks in a group.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Scatterv(const void *sendbuf, const int sendcounts[], const int displs[],
	       MPI_Datatype sendtype, void *recvbuf, int recvcount,
	       MPI_Datatype recvtype, int root, MPI_Comm comm)

	  int MPI_Iscatterv(const void *sendbuf, const int sendcounts[], const int displs[],
	       MPI_Datatype sendtype, void *recvbuf, int recvcount,
	       MPI_Datatype recvtype, int root, MPI_Comm comm, MPI_Request *request)

	  int MPI_Scatterv_init(const void *sendbuf, const int sendcounts[], const int displs[],
	       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_SCATTERV(SENDBUF, SENDCOUNTS, DISPLS, SENDTYPE, RECVBUF,
		       RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR)
	       <type>  SENDBUF(*), RECVBUF(*)
	       INTEGER SENDCOUNTS(*), DISPLS(*), SENDTYPE
	       INTEGER RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR

	  MPI_ISCATTERV(SENDBUF, SENDCOUNTS, DISPLS, SENDTYPE, RECVBUF,
		       RECVCOUNT, RECVTYPE, ROOT, COMM, REQUEST, IERROR)
	       <type>  SENDBUF(*), RECVBUF(*)
	       INTEGER SENDCOUNTS(*), DISPLS(*), SENDTYPE
	       INTEGER RECVCOUNT, RECVTYPE, ROOT, COMM, REQUEST, IERROR

	  MPI_SCATTERV_INIT(SENDBUF, SENDCOUNTS, DISPLS, SENDTYPE, RECVBUF,
		       RECVCOUNT, RECVTYPE, ROOT, COMM, INFO, REQUEST, IERROR)
	       <type>  SENDBUF(*), RECVBUF(*)
	       INTEGER SENDCOUNTS(*), DISPLS(*), SENDTYPE
	       INTEGER RECVCOUNT, RECVTYPE, ROOT, COMM, INFO, REQUEST, IERROR

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

	  MPI_Iscatterv(sendbuf, sendcounts, displs, sendtype, recvbuf, recvcount,
		       recvtype, root, comm, request, ierror)
	       TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
	       TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
	       INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), displs(*)
	       INTEGER, INTENT(IN) :: 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_scatterv_init(sendbuf, sendcounts, displs, sendtype, recvbuf, recvcount,
		       recvtype, root, comm, info, request, ierror)
	       TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
	       TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
	       INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), displs(*)
	       INTEGER, INTENT(IN) :: 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).

       • sendcounts: Integer array (of length group size) specifying the  number  of  elements	to  send  to  each
	 processor.

       • displs:  Integer  array  (of length group size). Entry i specifies the displacement (relative to sendbuf)
	 from which to take the outgoing data to process i.

       • sendtype: Datatype of send buffer elements (handle).

       • 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 only).

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

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

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

DESCRIPTION
       MPI_Scatterv <#mpi-scatterv> is the inverse operation to MPI_Gatherv <#mpi-gatherv>.

       MPI_Scatterv <#mpi-scatterv> extends the functionality of MPI_Scatter <#mpi-scatter> by allowing a  varying
       count of data to be sent to each process, since sendcounts is now an array. It also allows more flexibility
       as to where the data is taken from on the root, by providing the new argument, displs.

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

	  MPI_Send(sendbuf + displs[i] * extent(sendtype),
		   sendcounts[i], sendtype, i, ...);

	  // and each process executed a receive,

	  MPI_Recv(recvbuf, recvcount, recvtype, root, ...)

       The send buffer is ignored for all nonroot processes.

       The  type  signature  implied  by  sendcount[i],	 sendtype  at the root must be equal to the type signature
       implied by recvcount, recvtype at process i (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, types, and displacements should not cause any location on the root to be read
       more than once.

       Example 1: The reverse of Example 5 in the MPI_Gatherv <#mpi-gatherv> manpage. We  have	a  varying  stride
       between	blocks	at  sending  (root)  side,  at the receiving side we receive 100 - i elements into the ith
       column of a 100 x 150 C array at process i.

	  MPI_Comm comm;
	  int gsize,recvarray[100][150],*rptr;
	  int root, *sendbuf, myrank, bufsize, *stride;
	  MPI_Datatype rtype;
	  int i, *displs, *scounts, offset;
	  ...
	  MPI_Comm_size( comm, &gsize);
	  MPI_Comm_rank( comm, &myrank );

	  stride = (int *)malloc(gsize*sizeof(int));
	  ...
	  /* stride[i] for i = 0 to gsize-1 is set somehow
	   * sendbuf comes from elsewhere
	   */
	  ...
	  displs = (int *)malloc(gsize*sizeof(int));
	  scounts = (int *)malloc(gsize*sizeof(int));
	  offset = 0;
	  for (i=0; i<gsize; ++i) {
	      displs[i] = offset;
	      offset += stride[i];
	      scounts[i] = 100 - i;
	  }
	  /* Create datatype for the column we are receiving
	   */
	  MPI_Type_vector( 100-myrank, 1, 150, MPI_INT, &rtype);
	  MPI_Type_commit( &rtype );
	  rptr = &recvarray[0][myrank];
	  MPI_Scatterv(sendbuf, scounts, displs, MPI_INT,
		       rptr, 1, rtype, root, comm);

       Example 2: The reverse of Example 1 in the MPI_Gather manpage. The root process scatters sets of	 100  ints
       to  the	other  processes, but the sets of 100 are stride ints apart in the sending buffer. Requires use of
       MPI_Scatterv <#mpi-scatterv>, where stride >= 100.

	  MPI_Comm comm;
	  int gsize,*sendbuf;
	  int root, rbuf[100], i, *displs, *scounts;

	  ...

	  MPI_Comm_size(comm, &gsize);
	  sendbuf = (int *)malloc(gsize*stride*sizeof(int));
	  ...
	  displs = (int *)malloc(gsize*sizeof(int));
	  scounts = (int *)malloc(gsize*sizeof(int));
	  for (i=0; i<gsize; ++i) {
	     displs[i] = i*stride;
	     scounts[i] = 100;
	  }
	  MPI_Scatterv(sendbuf, scounts, displs, 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_Gather <#mpi-gather>

	  • MPI_Gatherv <#mpi-gatherv>

	  • MPI_Scatter <#mpi-scatter>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				      MPI_SCATTERV_INIT(3)
