MPIAllgatherv(3OpenMPI) MPIAllgatherv(3OpenMPI)

NAME
       MMPPIIAAllllggaatthheerrvv  -  Gathers  data  from all processes and delivers it to
       all. Each process may contribute a different amount of data.


SSYYNNTTAAXX
CC SSyynnttaaxx
       #include 
       int MPIAllgatherv(void *sendbuf, int sendcount,
            MPIDatatype sendtype, void *recvbuf, int *recvcount,
            int *displs, MPIDatatype recvtype, MPIComm comm)


FFoorrttrraann SSyynnttaaxx
       INCLUDE 'mpif.h'
       MPIALLGATHERV(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF,
                 RECVCOUNT, DISPLS, RECVTYPE, COMM, IERROR)
                SENDBUF(*), RECVBUF(*)
            INTEGER   SENDCOUNT, SENDTYPE, RECVCOUNT(*),
            INTEGER   DISPLS(*), RECVTYPE, COMM, IERROR


CC++++ SSyynnttaaxx
       #include 
       void MPI::Comm::Allgatherv(const void* sendbuf, int sendcount,
            const MPI::Datatype& sendtype, void* recvbuf,
            const int recvcounts[], const int displs[],
            const MPI::Datatype& recvtype) const = 0


IINNPPUUTT PPAARRAAMMEETTEERRSS
       sendbuf   Starting address of send buffer (choice).

       sendcount Number of elements in send buffer (integer).

       sendtype  Datatype of send buffer elements (handle).

       recvcount Integer array (of length group size) containing the number of
                 elements that are received from each process.

       displs    Integer  array  (of length group size). Entry i specifies the
                 displacement (relative to recvbuf)  at  which  to  place  the
                 incoming data from process i.

       recvtype  Datatype of receive buffer elements (handle).

       comm      Communicator (handle).


OOUUTTPPUUTT PPAARRAAMMEETTEERRSS
       recvbuf   Address of receive buffer (choice).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       MPIAllgatherv is similar to MPIAllgather in that all processes gather
       data from all other processes, except that each process can send a dif-
       ferent  amount  of data. The block of data sent from the jth process is
       received by every process and placed in the jth  block  of  the  buffer
       recvbuf.

       The  type  signature  associated with sendcount, sendtype, at process j
       must be equal to the  type  signature  associated  with  recvcounts[j],
       recvtype at any other process.

       The outcome is as if all processes executed calls to
       MPIGatherv(sendbuf,sendcount,sendtype,recvbuf,recvcount,
                   displs,recvtype,root,comm)

       for  root = 0 , ..., n-1. The rules for correct usage of MPIAllgatherv
       are easily found from the corresponding rules for MPIGatherv.


UUSSEE OOFF IINN-PPLLAACCEE OOPPTTIIOONN
       When the communicator is an intracommunicator, you can perform an  all-
       gather  operation  in-place  (the  output  buffer  is used as the input
       buffer).  Use the variable MPIINPLACE as the value  of  both  sendbuf
       and  recvbuf.   In  this case, sendcount and sendtype are ignored.  The
       input data of each process is assumed to be  in  the  area  where  that
       process  would  receive  its  own  contribution  to the receive buffer.
       Specifically, the outcome of a call to MPIAllgather that used the  in-
       place option is identical to the case in which all processes executed n
       calls to

          MPIGATHERV ( MPIINPLACE, 0, MPIDATATYPENULL, recvbuf,
          recvcounts, displs, recvtype, root, comm )

       for root =0, ... , n-1.

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

       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.


WWHHEENN CCOOMMMMUUNNIICCAATTOORR IISS AANN IINNTTEERR-CCOOMMMMUUNNIICCAATTOORR
       When  the  communicator  is an inter-communicator, the gather operation
       occurs in two phases.  The data is gathered from all the members of the
       first  group, concatenated, and received by all the members of the sec-
       ond group.  Then the data is gathered from all the members of the  sec-
       ond  group, concatenated, and received by all the members of the first.
       The send buffer arguments in the one group must be consistent with  the
       receive buffer arguments in the other group, and vice versa.  The oper-
       ation must exhibit symmetric, full-duplex behavior.

       The first group defines  the  root  process.   The  root  process  uses
       MPIROOT  as the value of root.  All other processes in the first group
       use MPIPROCNULL as the value of root.  All processes  in  the  second
       group  use the rank of the root process in the first group as the value
       of root.

       When the communicator is an intra-communicator, these  groups  are  the
       same, and the operation occurs in a single phase.



EERRRROORRSS
       Almost  all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last  argument.  C++  func-
       tions  do  not  return  errors.  If the default error handler is set to
       MPI::ERRORSTHROWEXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before  the  error  value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job,  except  for
       I/O   function   errors.   The   error  handler  may  be  changed  with
       MPICommseterrhandler; the predefined error handler MPIERRORSRETURN
       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.


SEE ALSO
       MPIGatherv
       MPIAllgather



Open MPI 1.2                      March 2007          MPIAllgatherv(3OpenMPI)