1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
.. _mpi_alltoallw:
MPI_Alltoallw
=============
.. include_body
:ref:`MPI_Alltoallw`, :ref:`MPI_Ialltoallw`, :ref:`MPI_Alltoallw_init` - All processes
send data of different types to, and receive data of different types
from, all processes
SYNTAX
------
C Syntax
^^^^^^^^
.. code-block:: c
#include <mpi.h>
int MPI_Alltoallw(const void *sendbuf, const int sendcounts[],
const int sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const int rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm)
int MPI_Ialltoallw(const void *sendbuf, const int sendcounts[],
const int sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const int rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm,
MPI_Request *request)
int MPI_Alltoallw_init(const void *sendbuf, const int sendcounts[],
const int sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const int rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm, MPI_Info info,
MPI_Request *request)
Fortran Syntax
^^^^^^^^^^^^^^
.. code-block:: fortran
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
INTEGER COMM, IERROR
MPI_IALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, REQUEST, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
INTEGER COMM, REQUEST, IERROR
MPI_ALLTOALLW_INIT(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, INFO, REQUEST, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
INTEGER COMM, INFO, REQUEST, IERROR
Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^
.. code-block:: fortran
USE mpi_f08
MPI_Alltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf, recvcounts,
rdispls, recvtypes, comm, ierror)
TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
TYPE(*), DIMENSION(..) :: recvbuf
INTEGER, INTENT(IN) :: sendcounts(*), sdispls(*), recvcounts(*),
rdispls(*)
TYPE(MPI_Datatype), INTENT(IN) :: sendtypes(*)
TYPE(MPI_Datatype), INTENT(IN) :: recvtypes(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Ialltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
recvcounts, rdispls, recvtypes, comm, request, ierror)
TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), sdispls(*),
recvcounts(*), rdispls(*)
TYPE(MPI_Datatype), INTENT(IN), ASYNCHRONOUS :: sendtypes(*),
recvtypes(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Request), INTENT(OUT) :: request
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Alltoallw_init(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
recvcounts, rdispls, recvtypes, comm, fIinfo, request, ierror)
TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), sdispls(*),
recvcounts(*), rdispls(*)
TYPE(MPI_Datatype), INTENT(IN), ASYNCHRONOUS :: sendtypes(*),
recvtypes(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Info), INTENT(IN) :: info
TYPE(MPI_Request), INTENT(OUT) :: request
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT PARAMETERS
----------------
* ``sendbuf``: Starting address of send buffer.
* ``sendcounts``: Integer array, where entry i specifies the number of elements to send to rank i.
* ``sdispls``: Integer array, where entry i specifies the displacement (in bytes, offset from *sendbuf) from which to send data to rank i.*
* ``sendtypes``: Datatype array, where entry i specifies the datatype to use when sending data to rank i.
* ``recvcounts``: Integer array, where entry j specifies the number of elements to receive from rank j.
* ``rdispls``: Integer array, where entry j specifies the displacement (in bytes, offset from *recvbuf) to which data from rank j should* be written.
* ``recvtypes``: Datatype array, where entry j specifies the datatype to use when receiving data from rank j.
* ``comm``: Communicator over which data is to be exchanged.
* ``info``: Info (handle, persistent only)
OUTPUT PARAMETERS
-----------------
* ``recvbuf``: Address of receive buffer.
* ``request``: Request (handle, non-blocking only).
* ``ierror``: Fortran only: Error status.
DESCRIPTION
-----------
:ref:`MPI_Alltoallw` is a generalized collective operation in which all
processes send data to and receive data from all other processes. It
adds flexibility to :ref:`MPI_Alltoallv` by allowing the user to specify the
datatype of individual data blocks (in addition to displacement and
element count). Its operation can be thought of in the following way,
where each process performs 2n (n being the number of processes in
communicator *comm) independent point-to-point communications*
(including communication with itself).
.. code-block:: c
MPI_Comm_size(comm, &n);
for (i = 0, i < n; i++)
MPI_Send(sendbuf + sdispls[i], sendcounts[i],
sendtypes[i], i, ..., comm);
for (i = 0, i < n; i++)
MPI_Recv(recvbuf + rdispls[i], recvcounts[i],
recvtypes[i], i, ..., comm);
Process j sends the k-th block of its local *sendbuf to process* k,
which places the data in the j-th block of its local *recvbuf.*
When a pair of processes exchanges data, each may pass different element
count and datatype arguments so long as the sender specifies the same
amount of data to send (in bytes) as the receiver expects to receive.
Note that process i may send a different amount of data to process j
than it receives from process j. Also, a process may send entirely
different amounts and types of data to different processes in the
communicator.
WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
When the communicator is an inter-communicator, the gather operation
occurs in two phases. The data is gathered from all the members of the
first group and received by all the members of the second group. Then
the data is gathered from all the members of the second group and
received by all the members of the first. The operation exhibits a
symmetric, full-duplex behavior.
The first group defines the root process. The root process uses MPI_ROOT
as the value of *root*. All other processes in the first group use
``MPI_PROC_NULL`` as the value of *root*. All processes in the second group
use the rank of the root process in the first group as the value of
*root*.
When the communicator is an intra-communicator, these groups are the
same, and the operation occurs in a single phase.
USE OF IN-PLACE OPTION
----------------------
When the communicator is an intracommunicator, you can perform an
all-to-all operation in-place (the output buffer is used as the input
buffer). Use the variable MPI_IN_PLACE as the value of *sendbuf*. In
this case, *sendcounts*, *sdispls*, and *sendtypes* are ignored. The
input data of each process is assumed to be in the area where that
process would receive its own contribution to the receive buffer.
NOTES
-----
The specification of counts, types, and displacements should not cause
any location to be written more than once.
All arguments on all processes are significant. The *comm* argument, in
particular, must describe the same communicator on all processes.
The offsets of *sdispls* and *rdispls* are measured in bytes. Compare
this to :ref:`MPI_Alltoallv`, where these offsets are measured in units of
*sendtype* and *recvtype*, respectively.
ERRORS
------
.. include:: ./ERRORS.rst
.. seealso::
* :ref:`MPI_Alltoall`
* :ref:`MPI_Alltoallv`
|
