Gathers data from all tasks and distribute it to all
int MPI_Allgather ( sendbuf, sendcount, sendtype,
recvbuf, recvcount, recvtype, comm )
- sendbuf - starting address of send buffer (choice)
- sendcount - number of elements in send buffer (integer)
- sendtype - data type of send buffer elements (handle)
- recvcount - number of elements received from any process (integer)
- recvtype - data type of receive buffer elements (handle)
- comm - communicator (handle)
- recvbuf - address of receive buffer (choice)
The MPI standard (1.0 and 1.1) says that
The jth block of data sent from
each proess is received by every process and placed in the jth block of the
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.
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
All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER
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_Errhandler_set; the predefined error handler
MPI_ERRORS_RETURN may be used to cause error values to be returned.
Note that MPI does not guarentee that an MPI program can continue past
- MPI_ERR_COMM - Invalid communicator. A common error is to use a null
communicator 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_Datatype (see MPI_Type_commit).
- MPI_ERR_TYPE - Invalid datatype argument. May be an uncommitted
- MPI_ERR_BUFFER - Invalid buffer pointer. Usually a null buffer where
one is not valid.