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MPI_Intercomm_create - Creates an intercommuncator from two intracommunicators
#include <mpi.h>
int MPI_Intercomm_create(MPI_Comm lcomm, int lleader,
MPI_Comm pcomm, int pleader, int tag,
MPI_Comm *newcomm)
lcomm
- Local (intra)communicator
lleader
- Rank in local_comm of leader (often 0)
pcomm
- Remote communicator
pleader
- Rank in peer_comm of remote leader (often 0)
tag
- Message tag to use in constructing intercommunicator; if multiple MPI_Intercomm_creates are being made, they should use different tags (more precisely, ensure that the local and remote leaders are using different
tags for each MPI_intercomm_create).
newcomm
- Created intercommunicator
The MPI 1.1 Standard contains two mutually exclusive comments on the input intracommunicators. One says that their repective
groups must be disjoint; the other that the leaders can be the same process. After some discussion by the MPI Forum, it has
been decided that the groups must be disjoint. Note that the reason given for this in the standard is not the reason
for this choice; rather, the other operations on intercommunicators (like MPI_Intercomm_merge) do not make sense if the groups are not disjoint.
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_TAG
- Invalid tag argument. Tags must be non-negative; tags in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_TAG.Thelargesttagvalueisavailable through the the attribute MPI_TAG_UB.
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.
MPI_ERR_RANK
- Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a
receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.
MPI_Intercomm_merge, MPI_Comm_free, MPI_Comm_remote_group, MPI_Comm_remote_size
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