[97] | 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_Get_elements 3 "Dec 08, 2009" "1.4" "Open MPI" |
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| 4 | .SH NAME |
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| 5 | \fBMPI_Get_elements \fP \- Returns the number of basic elements in a data type. |
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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_Get_elements(MPI_Status *\fIstatus\fP, MPI_Datatype\fI datatype\fP, |
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| 13 | int\fI *count\fP) |
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| 14 | |
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| 15 | .SH Fortran Syntax |
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| 16 | .nf |
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| 17 | INCLUDE 'mpif.h' |
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| 18 | MPI_GET_ELEMENTS(\fISTATUS, DATATYPE, COUNT, IERROR\fP) |
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| 19 | INTEGER \fISTATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR\fP |
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| 20 | |
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| 21 | .SH C++ Syntax |
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| 22 | .nf |
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| 23 | #include <mpi.h> |
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| 24 | int Status::Get_elements(const Datatype& \fIdatatype\fP) const |
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| 25 | |
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| 26 | .SH INPUT PARAMETERS |
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| 27 | .ft R |
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| 28 | .TP 1i |
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| 29 | status |
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| 30 | Return status of receive operation (status). |
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| 31 | .TP 1i |
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| 32 | datatype |
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| 33 | Datatype used by receive operation (handle). |
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| 34 | |
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| 35 | .SH OUTPUT PARAMETERS |
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| 36 | .ft R |
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| 37 | count Number of received basic elements (integer). |
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| 38 | .ft R |
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| 39 | .TP 1i |
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| 40 | IERROR |
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| 41 | Fortran only: Error status (integer). |
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| 42 | |
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| 43 | .SH DESCRIPTION |
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| 44 | .ft R |
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| 45 | MPI_Get_elements behaves different from MPI_Get_count, which returns the number of "top-level entries" received, i.e., the number of "copies" of type datatype. MPI_Get_count may return any integer value k, where 0 =< k =< count. If MPI_Get_count returns k, then the number of basic elements received (and the value returned by MPI_Get_elements) is n * k, where n is the number of basic elements in the type map of datatype. If the number of basic elements received is not a multiple of n, that is, if the receive operation has not received an integral number of datatype "copies," then MPI_Get_count returns the value MPI_UNDEFINED. |
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| 46 | .sp |
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| 47 | \fBExample:\fP Usage of MPI_Get_count and MPI_Get_element: |
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| 48 | .sp |
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| 49 | .nf |
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| 50 | \&... |
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| 51 | CALL MPI_TYPE_CONTIGUOUS(2, MPI_REAL, Type2, ierr) |
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| 52 | CALL MPI_TYPE_COMMIT(Type2, ierr) |
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| 53 | \&... |
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| 54 | CALL MPI_COMM_RANK(comm, rank, ierr) |
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| 55 | IF(rank.EQ.0) THEN |
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| 56 | CALL MPI_SEND(a, 2, MPI_REAL, 1, 0, comm, ierr) |
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| 57 | CALL MPI_SEND(a, 3, MPI_REAL, 1, 0, comm, ierr) |
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| 58 | ELSE |
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| 59 | CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) |
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| 60 | CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=1 |
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| 61 | CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=2 |
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| 62 | CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) |
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| 63 | CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=MPI_UNDEFINED |
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| 64 | CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=3 |
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| 65 | END IF |
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| 66 | .fi |
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| 67 | .sp |
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| 68 | The function MPI_Get_elements can also be used after a probe to find the number of elements in the probed message. Note that the two functions MPI_Get_count and MPI_Get_elements return the same values when they are used with primitive data types. |
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| 69 | |
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| 70 | .SH ERRORS |
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| 71 | 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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| 72 | .sp |
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| 73 | Before the error value is returned, the current MPI error handler is |
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| 74 | 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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| 75 | |
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| 76 | .SH SEE ALSO |
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| 77 | .ft R |
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| 78 | .sp |
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| 79 | MPI_Get_count |
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| 80 | |
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