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MPI_Comm_size
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Determines the size of the group associated with a communicator
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Synopsis
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int MPI_Comm_size(MPI_Comm comm, int *size)
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Input Parameters
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comm communicator (handle)
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Output Parameters
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size number of processes in the group of <tt>comm</tt> (integer)
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Notes
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Null Handles
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The MPI 1.1 specification, in the section on opaque objects, explicitly
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disallows freeing a null communicator. The text from the standard is:
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A null handle argument is an erroneous IN argument in MPI calls, unless an
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exception is explicitly stated in the text that defines the function. Such
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exception is allowed for handles to request objects in Wait and Test calls
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(sections Communication Completion and Multiple Completions ). Otherwise, a
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null handle can only be passed to a function that allocates a new object and
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returns a reference to it in the handle.
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Thread and Interrupt Safety
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This routine is both thread- and interrupt-safe.
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This means that this routine may safely be used by multiple threads and
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from within a signal handler.
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Notes for Fortran
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All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
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an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
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</tt>is an integer and has the same meaning as the return value of the routine
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in C. In Fortran, MPI routines are subroutines, and are invoked with the
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<tt>call</tt> statement.
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All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
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</tt>in Fortran.
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Errors
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All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
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C routines as the value of the function and Fortran routines in the last
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argument. Before the value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job. The error handler
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may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
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<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
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RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
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its use is deprecated. The predefined error handler
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<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
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Note that MPI does not guarentee that an MPI program can continue past
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an error; however, MPI implementations will attempt to continue whenever
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possible.
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MPI_SUCCESS No error; MPI routine completed successfully.
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MPI_ERR_COMM Invalid communicator. A common error is to use a null
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communicator in a call (not even allowed in <tt>MPI_Comm_rank</tt>).
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MPI_ERR_ARG Invalid argument. Some argument is invalid and is not
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identified by a specific error class (e.g., <tt>MPI_ERR_RANK</tt>).
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