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MPI_Gatherv - Gathers into specified locations from all processes in a group
#include <mpi.h>
int MPI_Gatherv(void *sbuf, int scount, MPI_Datatype sdtype,
void *rbuf, int *rcounts, int *disps,
MPI_Datatype rdtype, int root, MPI_Comm comm)
sendbuf
- starting address of send buffer (choice)
sendcount
- number of elements in send buffer (integer)
sendtype
- data type of send buffer elements (handle)
recvcounts
- integer array (of length group size) containing the number of elements that are received from each process (significant
only at root)
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 (significant only at root)
recvtype
- data type of recv buffer elements (significant only at root) (handle)
root
- rank of receiving process (integer)
comm
- communicator (handle)
recvbuf
- address of receive buffer (choice, significant only at root)
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.
If an error occurs in an MPI function, the current MPI error handler is called to handle it. 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 (in C and Fortran; this error handler is less useful in with the C++ MPI
bindings. The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value needs to be
recovered). Note that MPI does not guarantee that an MPI program can continue past an error.
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. The C++ bindings
for MPI do not return error values; instead, error values are communicated by throwing exceptions of type MPI::Exception
(but not by default). Exceptions are only thrown if the error value is not MPI::SUCCESS.
Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return upon an error, there will be
no way to recover what the actual error value was.
MPI_SUCCESS
- No error; MPI routine completed successfully.
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_TYPE
- Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
MPI_ERR_BUFFER
- Invalid buffer pointer. Usually a null buffer where one is not valid.
MPI_ERR_ROOT
- Invalid root. The root must be specified as a rank in the communicator. Ranks must be between zero and the size of the
communicator minus one.
MPI_ERR_ARG
- Invalid argument. Some argument is invalid and is not identified by a specific error class. This is typically a NULL
pointer or other such error.
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