mirror of https://gitee.com/openkylin/openmpi.git
89 lines
2.8 KiB
Plaintext
89 lines
2.8 KiB
Plaintext
.\" -*- nroff -*-
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.\" Copyright 2010 Cisco Systems, Inc. All rights reserved.
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.\" Copyright 2006-2008 Sun Microsystems, Inc.
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.\" Copyright (c) 1996 Thinking Machines Corporation
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.\" $COPYRIGHT$
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.TH MPI_Comm_size 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
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.SH NAME
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\fBMPI_Comm_size \fP \- Returns the size of the group associated with a communicator.
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.SH SYNTAX
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.ft R
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.SH C Syntax
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.nf
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#include <mpi.h>
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int MPI_Comm_size(MPI_Comm \fIcomm\fP, int *\fIsize\fP)
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.fi
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.SH Fortran Syntax
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.nf
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USE MPI
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! or the older form: INCLUDE 'mpif.h'
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MPI_COMM_SIZE(\fICOMM, SIZE, IERROR\fP)
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INTEGER \fICOMM, SIZE, IERROR\fP
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.fi
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.SH Fortran 2008 Syntax
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.nf
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USE mpi_f08
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MPI_Comm_size(\fIcomm\fP, \fIsize\fP, \fIierror\fP)
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TYPE(MPI_Comm), INTENT(IN) :: \fIcomm\fP
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INTEGER, INTENT(OUT) :: \fIsize\fP
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INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP
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.fi
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.SH C++ Syntax
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.nf
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#include <mpi.h>
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int Comm::Get_size() const
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.fi
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.SH INPUT PARAMETER
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.ft R
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.TP 1i
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comm
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Communicator (handle).
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.SH OUTPUT PARAMETERS
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.ft R
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.TP 1i
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size
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Number of processes in the group of comm (integer).
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.ft R
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.TP 1i
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IERROR
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Fortran only: Error status (integer).
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.SH DESCRIPTION
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.ft R
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This function indicates the number of processes involved in a
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communicator. For MPI_COMM_WORLD, it indicates the total number of
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processes available. This function is equivalent to accessing the
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communicator's group with MPI_Comm_group, computing the size using
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MPI_Group_size, and then freeing the temporary group via
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MPI_Group_free. If the communicator is an inter-communicator (enables
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communication between two groups), this function returns the size of
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the local group. To return the size of the remote group, use the
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MPI_Comm_remote_size function.
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.sp
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This call is often used with MPI_Comm_rank to determine the amount of concurrency available for a specific library or program. MPI_Comm_rank indicates the rank of the process that calls it in the range from 0 . . . size-1, where size is the return value of MPI_Comm_size.
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.SH NOTE
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.ft R
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MPI_COMM_NULL is not considered a valid argument to this function.
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.SH ERRORS
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Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
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.sp
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Before the error value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.
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.SH SEE ALSO
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.ft R
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.sp
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.nf
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MPI_Comm_group
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MPI_Comm_rank
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MPI_Comm_compare
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