1MPI_Allgather(3) LAM/MPI MPI_Allgather(3)
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6 MPI_Allgather - Gathers data from all tasks and distribute it to all
7
9 #include <mpi.h>
10 int MPI_Allgather(void *sbuf, int scount, MPI_Datatype sdtype,
11 void *rbuf, int rcount, MPI_Datatype rdtype,
12 MPI_Comm comm)
13
15 sbuf - starting address of send buffer (choice)
16 scount - number of elements in send buffer (integer)
17 sdtype - data type of send buffer elements (handle)
18 rbuf - starting address of receive buffer (choice)
19 rcount - number of elements received from any process (integer)
20 rdtype - data type of receive buffer elements (handle)
21 comm - communicator (handle)
22
25 rbuf - address of receive buffer (choice)
26
29 The MPI standard (1.0 and 1.1) says
30 "The jth block of data sent from each proess is received by every
32 process and placed in the jth block of the buffer recvbuf."
33 This is misleading; a better description is
35 "The block of data sent from the jth process is received by every
37 process and placed in the jth block of the buffer recvbuf."
38 This text was suggested by Rajeev Thakur.
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43 LAM/MPI does not yet support invoking this function on a communicator
44 that contains ranks that are non-local IMPI procs.
45
48 All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
49 an additional argument ierr at the end of the argument list. ierr is
50 an integer and has the same meaning as the return value of the routine
51 in C. In Fortran, MPI routines are subroutines, and are invoked with
52 the call statement.
53 All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
55 Fortran.
56
59 If an error occurs in an MPI function, the current MPI error handler is
60 called to handle it. By default, this error handler aborts the MPI
61 job. The error handler may be changed with MPI_Errhandler_set ; the
62 predefined error handler MPI_ERRORS_RETURN may be used to cause error
63 values to be returned (in C and Fortran; this error handler is less
64 useful in with the C++ MPI bindings. The predefined error handler
65 MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value
66 needs to be recovered). Note that MPI does not guarantee that an MPI
67 program can continue past an error.
68 All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
70 value; C routines as the value of the function and Fortran routines in
71 the last argument. The C++ bindings for MPI do not return error val‐
72 ues; instead, error values are communicated by throwing exceptions of
73 type MPI::Exception (but not by default). Exceptions are only thrown
74 if the error value is not MPI::SUCCESS .
75 Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI
78 functions will return upon an error, there will be no way to recover
79 what the actual error value was.
80 MPI_ERR_COMM
81 - Invalid communicator. A common error is to use a null commu‐
82 nicator in a call (not even allowed in MPI_Comm_rank ).
83 MPI_ERR_OTHER
84 - A collective implementation was not able to be located at run-
85 time for this communicator.
86 MPI_ERR_COUNT
87 - Invalid count argument. Count arguments must be non-negative;
88 a count of zero is often valid.
89 MPI_ERR_TYPE
90 - Invalid datatype argument. May be an uncommitted MPI_Datatype
91 (see MPI_Type_commit ).
92 MPI_ERR_BUFFER
93 - Invalid buffer pointer. Usually a null buffer where one is
94 not valid.
95
98 For more information, please see the official MPI Forum web site, which
99 contains the text of both the MPI-1 and MPI-2 standards. These docu‐
100 ments contain detailed information about each MPI function (most of
101 which is not duplicated in these man pages).
102 http://www.mpi-forum.org/
104
108 The LAM Team would like the thank the MPICH Team for the handy program
109 to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sow‐
110 ing/sowing.tar.gz ), the initial formatting, and some initial text for
111 most of the MPI-1 man pages.
112
114 allgather.c
115LAM/MPI 7.1.2 2/23/2006 MPI_Allgather(3)