mac mpi

macx64/mpi/mpich/share/man/man3/MPI_Comm_split.3

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+.TH MPI_Comm_split 3 "6/5/2019" " " "MPI"
+.SH NAME
+MPI_Comm_split \-  Creates new communicators based on colors and keys 
+.SH SYNOPSIS
+.nf
+int MPI_Comm_split(MPI_Comm comm, int color, int key, MPI_Comm * newcomm)
+.fi
+.SH INPUT PARAMETERS
+.PD 0
+.TP
+.B comm 
+- communicator (handle)
+.PD 1
+.PD 0
+.TP
+.B color 
+- control of subset assignment (nonnegative integer).  Processes
+with the same color are in the same new communicator
+.PD 1
+.PD 0
+.TP
+.B key 
+- control of rank assignment (integer)
+.PD 1
+
+.SH OUTPUT PARAMETERS
+.PD 0
+.TP
+.B newcomm 
+- new communicator (handle)
+.PD 1
+
+.SH NOTES
+The 
+.I color
+must be non-negative or 
+.I MPI_UNDEFINED
+\&.
+
+
+.SH THREAD AND INTERRUPT SAFETY
+
+This routine is thread-safe.  This means that this routine may be
+safely used by multiple threads without the need for any user-provided
+thread locks.  However, the routine is not interrupt safe.  Typically,
+this is due to the use of memory allocation routines such as 
+.I malloc
+or other non-MPICH runtime routines that are themselves not interrupt-safe.
+
+.SH NOTES FOR FORTRAN
+All MPI routines in Fortran (except for 
+.I MPI_WTIME
+and 
+.I MPI_WTICK
+) have
+an additional argument 
+.I ierr
+at the end of the argument list.  
+.I 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
+.I call
+statement.
+
+All MPI objects (e.g., 
+.I MPI_Datatype
+, 
+.I MPI_Comm
+) are of type 
+.I INTEGER
+in Fortran.
+
+.SH ALGORITHM
+.nf
+1. Use MPI_Allgather to get the color and key from each process
+2. Count the number of processes with the same color; create a
+communicator with that many processes.  If this process has
+.I MPI_UNDEFINED
+as the color, create a process with a single member.
+3. Use key to order the ranks
+.fi
+
+
+.SH ERRORS
+
+All MPI routines (except 
+.I MPI_Wtime
+and 
+.I 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 
+.I MPI_Comm_set_errhandler
+(for communicators),
+.I MPI_File_set_errhandler
+(for files), and 
+.I MPI_Win_set_errhandler
+(for
+RMA windows).  The MPI-1 routine 
+.I MPI_Errhandler_set
+may be used but
+its use is deprecated.  The predefined error handler
+.I MPI_ERRORS_RETURN
+may be used to cause error values to be returned.
+Note that MPI does 
+.B not
+guarentee that an MPI program can continue past
+an error; however, MPI implementations will attempt to continue whenever
+possible.
+
+.PD 0
+.TP
+.B MPI_SUCCESS 
+- No error; MPI routine completed successfully.
+.PD 1
+.PD 0
+.TP
+.B MPI_ERR_COMM 
+- Invalid communicator.  A common error is to use a null
+communicator in a call (not even allowed in 
+.I MPI_Comm_rank
+).
+.PD 1
+.PD 0
+.TP
+.B MPI_ERR_INTERN 
+- This error is returned when some part of the MPICH 
+implementation is unable to acquire memory.  
+.PD 1
+
+.SH SEE ALSO
+MPI_Comm_free
+.br