1 | .\"Copyright 2006-2008 Sun Microsystems, Inc. |
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2 | .\" Copyright (c) 1996 Thinking Machines Corporation |
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3 | .TH MPI_Comm_size 3 "Dec 08, 2009" "1.4" "Open MPI" |
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4 | .SH NAME |
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5 | \fBMPI_Comm_size \fP \- Returns the size of the group associated with a communicator. |
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6 | |
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7 | .SH SYNTAX |
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8 | .ft R |
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9 | .SH C Syntax |
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10 | .nf |
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11 | #include <mpi.h> |
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12 | int MPI_Comm_size(MPI_Comm \fIcomm\fP, int *\fIsize\fP) |
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13 | |
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14 | .SH Fortran Syntax |
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15 | .nf |
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16 | INCLUDE 'mpif.h' |
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17 | MPI_COMM_SIZE(\fICOMM, SIZE, IERROR\fP) |
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18 | INTEGER \fICOMM, SIZE, IERROR\fP |
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19 | |
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20 | .SH C++ Syntax |
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21 | .nf |
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22 | #include <mpi.h> |
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23 | int Comm::Get_size() const |
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24 | |
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25 | .SH INPUT PARAMETER |
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26 | .ft R |
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27 | .TP 1i |
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28 | comm |
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29 | Communicator (handle). |
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30 | |
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31 | .SH OUTPUT PARAMETERS |
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32 | .ft R |
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33 | .TP 1i |
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34 | size |
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35 | Number of processes in the group of comm (integer). |
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36 | .ft R |
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37 | .TP 1i |
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38 | IERROR |
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39 | Fortran only: Error status (integer). |
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40 | |
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41 | .SH DESCRIPTION |
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42 | .ft R |
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43 | This function indicates the number of processes |
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44 | involved in a communicator. For MPI_COMM_WORLD, it indicates the total number of processes available. This function is equivalent to accessing the |
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45 | communicator's group with MPI_Comm_group, computing the size using MPI_Group_size, and then freeing the temporary group via MPI_Group_free. If the communicator is an intra-communicator (enables communication between two groups), this function returns the size of the local group. To return the size of the remote group, use the MPI_Comm_remote_size function. |
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46 | .sp |
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47 | 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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48 | |
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49 | .SH NOTE |
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50 | .ft R |
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51 | MPI_COMM_NULL is not considered a valid argument to this function. |
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52 | |
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53 | .SH ERRORS |
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54 | 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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55 | .sp |
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56 | Before the error value is returned, the current MPI error handler is |
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57 | 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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58 | |
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59 | .SH SEE ALSO |
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60 | .ft R |
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61 | .sp |
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62 | .nf |
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63 | MPI_Comm_group |
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64 | MPI_Comm_rank |
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65 | MPI_Comm_compare |
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66 | |
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