1MPI_Reduce_scatter(3) LAM/MPI MPI_Reduce_scatter(3)
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6 MPI_Reduce_scatter - Combines values and scatters the results
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9 #include <mpi.h>
10 int MPI_Reduce_scatter(void *sbuf, void *rbuf, int *rcounts,
11 MPI_Datatype dtype, MPI_Op op, MPI_Comm comm)
12
14 sbuf - starting address of send buffer (choice)
15 rcounts
16 - integer array specifying the number of elements in result dis‐
17 tributed to each process. Array must be identical on all call‐
18 ing processes.
19 dtype - data type of elements of input buffer (handle)
20 op - operation (handle)
21 comm - communicator (handle)
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25 rbuf - starting address of receive buffer (choice)
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29 LAM/MPI does not yet support invoking this function on a communicator
30 that contains ranks that are non-local IMPI procs.
31
34 All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
35 an additional argument ierr at the end of the argument list. ierr is
36 an integer and has the same meaning as the return value of the routine
37 in C. In Fortran, MPI routines are subroutines, and are invoked with
38 the call statement.
39 All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
41 Fortran.
42
45 The reduction functions ( MPI_Op ) do not return an error value. As a
46 result, if the functions detect an error, all they can do is either
47 call MPI_Abort or silently skip the problem. Thus, if you change the
48 error handler from MPI_ERRORS_ARE_FATAL to something else (e.g.,
49 MPI_ERRORS_RETURN ), then no error may be indicated.
50 The reason for this is the performance problems that arise in ensuring
52 that all collective routines return the same error value.
53
56 If an error occurs in an MPI function, the current MPI error handler is
57 called to handle it. By default, this error handler aborts the MPI
58 job. The error handler may be changed with MPI_Errhandler_set ; the
59 predefined error handler MPI_ERRORS_RETURN may be used to cause error
60 values to be returned (in C and Fortran; this error handler is less
61 useful in with the C++ MPI bindings. The predefined error handler
62 MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value
63 needs to be recovered). Note that MPI does not guarantee that an MPI
64 program can continue past an error.
65 All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
67 value; C routines as the value of the function and Fortran routines in
68 the last argument. The C++ bindings for MPI do not return error val‐
69 ues; instead, error values are communicated by throwing exceptions of
70 type MPI::Exception (but not by default). Exceptions are only thrown
71 if the error value is not MPI::SUCCESS .
72 Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI
75 functions will return upon an error, there will be no way to recover
76 what the actual error value was.
77 MPI_SUCCESS
78 - No error; MPI routine completed successfully.
79 MPI_ERR_COMM
80 - Invalid communicator. A common error is to use a null commu‐
81 nicator in a call (not even allowed in MPI_Comm_rank ).
82 MPI_ERR_OTHER
83 - A collective implementation was not able to be located at run-
84 time for this communicator.
85 MPI_ERR_OTHER
86 - A communicator that contains some non-local IMPI procs was
87 used for some function which has not yet had the IMPI extensions
88 implemented yet. For example, most collectives on IMPI communi‐
89 cators have not been implemented yet.
90 MPI_ERR_COUNT
91 - Invalid count argument. Count arguments must be non-negative;
92 a count of zero is often valid.
93 MPI_ERR_TYPE
94 - Invalid datatype argument. May be an uncommitted MPI_Datatype
95 (see MPI_Type_commit ).
96 MPI_ERR_BUFFER
97 - Invalid buffer pointer. Usually a null buffer where one is
98 not valid.
99 MPI_ERR_OP
100 - Invalid operation. MPI operations (objects of type MPI_Op )
101 must either be one of the predefined operations (e.g., MPI_SUM )
102 or created with MPI_Op_create . Additionally, only certain
103 datatypes are alloed with given predefined operations. See
104 MPI-1, section 4.9.2.
105 MPI_ERR_BUFFER
106 - Invalid buffer pointer. Usually a null buffer where one is
107 not valid.
108 MPI_ERR_BUFFER
109 - This error class is associcated with an error code that indi‐
110 cates that two buffer arguments are aliased ; that is, the
111 describe overlapping storage (often the exact same storage).
112 This is prohibited in MPI (because it is prohibited by the For‐
113 tran standard, and rather than have a separate case for C and
114 Fortran, the MPI Forum adopted the more restrictive requirements
115 of Fortran).
116
119 For more information, please see the official MPI Forum web site, which
120 contains the text of both the MPI-1 and MPI-2 standards. These docu‐
121 ments contain detailed information about each MPI function (most of
122 which is not duplicated in these man pages).
123 http://www.mpi-forum.org/
125
129 The LAM Team would like the thank the MPICH Team for the handy program
130 to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sow‐
131 ing/sowing.tar.gz ), the initial formatting, and some initial text for
132 most of the MPI-1 man pages.
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135 reducescatter.c
136LAM/MPI 7.1.2 2/23/2006 MPI_Reduce_scatter(3)