221 lines
7.0 KiB
Groff
221 lines
7.0 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_GET_ELEMENTS" "3" "Feb 14, 2025" "" "Open MPI"
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.sp
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\fI\%MPI_Get_elements\fP, \fI\%MPI_Get_elements_x\fP \- Returns the number of basic
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elements in a data type.
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.SH SYNTAX
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.SS C Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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#include <mpi.h>
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int MPI_Get_elements(const MPI_Status *status, MPI_Datatype datatype,
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int *count)
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int MPI_Get_elements_x(const MPI_Status *status, MPI_Datatype datatype,
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MPI_Count *count)
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE MPI
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! or the older form: INCLUDE \(aqmpif.h\(aq
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MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR)
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INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR
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MPI_GET_ELEMENTS_X(STATUS, DATATYPE, COUNT, IERROR)
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INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE
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INTEGER(KIND=MPI_COUNT_KIND) COUNT
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INTEGER IERROR
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran 2008 Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE mpi_f08
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MPI_Get_elements(status, datatype, count, ierror)
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TYPE(MPI_Status), INTENT(IN) :: status
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TYPE(MPI_Datatype), INTENT(IN) :: datatype
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INTEGER, INTENT(OUT) :: count
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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MPI_Get_elements_x(status, datatype, count, ierror)
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TYPE(MPI_Status), INTENT(IN) :: status
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TYPE(MPI_Datatype), INTENT(IN) :: datatype
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INTEGER(KIND = MPI_COUNT_KIND), INTENT(OUT) :: count
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SH INPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBstatus\fP : Return status of receive operation (status).
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.IP \(bu 2
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\fBdatatype\fP : Datatype used by receive operation (handle).
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.UNINDENT
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.SH OUTPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBierror\fP : Fortran only: Error status (integer).
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.UNINDENT
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.SH DESCRIPTION
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.sp
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\fI\%MPI_Get_elements\fP and \fI\%MPI_Get_elements_x\fP behave different from
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\fI\%MPI_Get_count\fP, which returns the number of “top\-level entries” received,
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i.e., the number of “copies” of type datatype. \fI\%MPI_Get_count\fP may return
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any integer value k, where 0 =< k =< count. If \fI\%MPI_Get_count\fP returns k,
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then the number of basic elements received (and the value returned by
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\fI\%MPI_Get_elements\fP and MPI_Get_elements_x) is n k, where n is the number
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of basic elements in the type map of datatype. If the number of basic
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elements received is not a multiple of n, that is, if the receive
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operation has not received an integral number of datatype “copies,” then
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\fI\%MPI_Get_count\fP returns the value MPI_UNDEFINED. For both functions, if
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the count parameter cannot express the value to be returned (e.g., if
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the parameter is too small to hold the output value), it is set to
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MPI_UNDEFINED.
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.sp
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Example: Usage of \fI\%MPI_Get_count\fP and \fI\%MPI_Get_elements\fP:
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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call MPI_TYPE_CONTIGUOUS(2, MPI_REAL, Type2, ierr)
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call MPI_TYPE_COMMIT(Type2, ierr)
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call MPI_COMM_RANK(comm, rank, ierr)
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IF ( rank == 0 ) THEN
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CALL MPI_SEND(a, 2, MPI_REAL, 1, 0, comm, ierr)
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CALL MPI_SEND(a, 3, MPI_REAL, 1, 0, comm, ierr)
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ELSE
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CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr)
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CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=1
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CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=2
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CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr)
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CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=MPI_UNDEFINED
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CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=3
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END IF
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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The function \fI\%MPI_Get_elements\fP can also be used after a probe to find the
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number of elements in the probed message. Note that the two functions
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\fI\%MPI_Get_count\fP and \fI\%MPI_Get_elements\fP return the same values when they are
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used with primitive data types.
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.SH ERRORS
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.sp
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Almost all MPI routines return an error value; C routines as the return result
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of the function and Fortran routines in the last argument.
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.sp
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Before the error value is returned, the current MPI error handler associated
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with the communication object (e.g., communicator, window, file) is called.
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If no communication object is associated with the MPI call, then the call is
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considered attached to MPI_COMM_SELF and will call the associated MPI error
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handler. When MPI_COMM_SELF is not initialized (i.e., before
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\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
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Model exclusively) the error raises the initial error handler. The initial
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error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
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MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
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argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
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error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
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handler is called for all other MPI functions.
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.sp
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Open MPI includes three predefined error handlers that can be used:
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.INDENT 0.0
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.IP \(bu 2
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\fBMPI_ERRORS_ARE_FATAL\fP
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Causes the program to abort all connected MPI processes.
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.IP \(bu 2
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\fBMPI_ERRORS_ABORT\fP
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An error handler that can be invoked on a communicator,
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window, file, or session. When called on a communicator, it
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acts as if \fI\%MPI_Abort\fP was called on that communicator. If
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called on a window or file, acts as if \fI\%MPI_Abort\fP was called
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on a communicator containing the group of processes in the
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corresponding window or file. If called on a session,
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aborts only the local process.
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.IP \(bu 2
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\fBMPI_ERRORS_RETURN\fP
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Returns an error code to the application.
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.UNINDENT
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.sp
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MPI applications can also implement their own error handlers by calling:
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
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.IP \(bu 2
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\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.UNINDENT
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.sp
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Note that MPI does not guarantee that an MPI program can continue past
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an error.
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.sp
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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.sp
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See the Error Handling section of the MPI\-3.1 standard for
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more information.
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.sp
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\fBSEE ALSO:\fP
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.INDENT 0.0
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.INDENT 3.5
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\fI\%MPI_Get_count\fP
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.UNINDENT
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.UNINDENT
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.SH COPYRIGHT
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2003-2025, The Open MPI Community
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.\" Generated by docutils manpage writer.
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.
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