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<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_free.3.html">17.2.58. MPI_Comm_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_free_keyval.3.html">17.2.59. MPI_Comm_free_keyval</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_get_attr.3.html">17.2.60. MPI_Comm_get_attr</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_get_errhandler.3.html">17.2.61. MPI_Comm_get_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_get_info.3.html">17.2.62. MPI_Comm_get_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_get_name.3.html">17.2.63. MPI_Comm_get_name</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_get_parent.3.html">17.2.64. MPI_Comm_get_parent</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_group.3.html">17.2.65. MPI_Comm_group</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_idup.3.html">17.2.66. MPI_Comm_idup</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_idup_with_info.3.html">17.2.67. MPI_Comm_idup_with_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_join.3.html">17.2.68. MPI_Comm_join</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_rank.3.html">17.2.69. MPI_Comm_rank</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_remote_group.3.html">17.2.70. MPI_Comm_remote_group</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_remote_size.3.html">17.2.71. MPI_Comm_remote_size</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_set_attr.3.html">17.2.72. MPI_Comm_set_attr</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_set_errhandler.3.html">17.2.73. MPI_Comm_set_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_set_info.3.html">17.2.74. MPI_Comm_set_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_set_name.3.html">17.2.75. MPI_Comm_set_name</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_size.3.html">17.2.76. MPI_Comm_size</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_spawn.3.html">17.2.77. MPI_Comm_spawn</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_spawn_multiple.3.html">17.2.78. MPI_Comm_spawn_multiple</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_split.3.html">17.2.79. MPI_Comm_split</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_split_type.3.html">17.2.80. MPI_Comm_split_type</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Comm_test_inter.3.html">17.2.81. MPI_Comm_test_inter</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Compare_and_swap.3.html">17.2.82. MPI_Compare_and_swap</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Dims_create.3.html">17.2.83. MPI_Dims_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Dist_graph_create.3.html">17.2.84. MPI_Dist_graph_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Dist_graph_create_adjacent.3.html">17.2.85. MPI_Dist_graph_create_adjacent</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Dist_graph_neighbors.3.html">17.2.86. MPI_Dist_graph_neighbors</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Dist_graph_neighbors_count.3.html">17.2.87. MPI_Dist_graph_neighbors_count</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Errhandler_create.3.html">17.2.88. MPI_Errhandler_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Errhandler_free.3.html">17.2.89. MPI_Errhandler_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Errhandler_get.3.html">17.2.90. MPI_Errhandler_get</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Errhandler_set.3.html">17.2.91. MPI_Errhandler_set</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Errors.3.html">17.2.92. MPI Errors</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Error_class.3.html">17.2.93. MPI_Error_class</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Error_string.3.html">17.2.94. MPI_Error_string</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Exscan.3.html">17.2.95. MPI_Exscan</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Exscan_init.3.html">17.2.96. MPI_Exscan_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Fetch_and_op.3.html">17.2.97. MPI_Fetch_and_op</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_c2f.3.html">17.2.98. MPI_File_c2f</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_call_errhandler.3.html">17.2.99. MPI_File_call_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_close.3.html">17.2.100. MPI_File_close</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_create_errhandler.3.html">17.2.101. MPI_File_create_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_delete.3.html">17.2.102. MPI_File_delete</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_f2c.3.html">17.2.103. MPI_File_f2c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_amode.3.html">17.2.104. MPI_File_get_amode</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_atomicity.3.html">17.2.105. MPI_File_get_atomicity</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_byte_offset.3.html">17.2.106. MPI_File_get_byte_offset</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_errhandler.3.html">17.2.107. MPI_File_get_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_group.3.html">17.2.108. MPI_File_get_group</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_info.3.html">17.2.109. MPI_File_get_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_position.3.html">17.2.110. MPI_File_get_position</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_position_shared.3.html">17.2.111. MPI_File_get_position_shared</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_size.3.html">17.2.112. MPI_File_get_size</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_type_extent.3.html">17.2.113. MPI_File_get_type_extent</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_get_view.3.html">17.2.114. MPI_File_get_view</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iread.3.html">17.2.115. MPI_File_iread</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iread_all.3.html">17.2.116. MPI_File_iread_all</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iread_at.3.html">17.2.117. MPI_File_iread_at</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iread_at_all.3.html">17.2.118. MPI_File_iread_at_all</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iread_shared.3.html">17.2.119. MPI_File_iread_shared</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iwrite.3.html">17.2.120. MPI_File_iwrite</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iwrite_all.3.html">17.2.121. MPI_File_iwrite_all</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iwrite_at.3.html">17.2.122. MPI_File_iwrite_at</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iwrite_at_all.3.html">17.2.123. MPI_File_iwrite_at_all</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_iwrite_shared.3.html">17.2.124. MPI_File_iwrite_shared</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_open.3.html">17.2.125. MPI_File_open</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_preallocate.3.html">17.2.126. MPI_File_preallocate</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read.3.html">17.2.127. MPI_File_read</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_all.3.html">17.2.128. MPI_File_read_all</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_all_begin.3.html">17.2.129. MPI_File_read_all_begin</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_all_end.3.html">17.2.130. MPI_File_read_all_end</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_at.3.html">17.2.131. MPI_File_read_at</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_at_all.3.html">17.2.132. MPI_File_read_at_all</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_at_all_begin.3.html">17.2.133. MPI_File_read_at_all_begin</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_at_all_end.3.html">17.2.134. MPI_File_read_at_all_end</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_ordered.3.html">17.2.135. MPI_File_read_ordered</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_ordered_begin.3.html">17.2.136. MPI_File_read_ordered_begin</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_ordered_end.3.html">17.2.137. MPI_File_read_ordered_end</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_read_shared.3.html">17.2.138. MPI_File_read_shared</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_seek.3.html">17.2.139. MPI_File_seek</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_seek_shared.3.html">17.2.140. MPI_File_seek_shared</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_File_set_info.3.html">17.2.143. MPI_File_set_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_set_size.3.html">17.2.144. MPI_File_set_size</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_set_view.3.html">17.2.145. MPI_File_set_view</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_File_write_all_begin.3.html">17.2.149. MPI_File_write_all_begin</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_File_write_at.3.html">17.2.151. MPI_File_write_at</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_write_at_all.3.html">17.2.152. MPI_File_write_at_all</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_write_at_all_begin.3.html">17.2.153. MPI_File_write_at_all_begin</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_write_at_all_end.3.html">17.2.154. MPI_File_write_at_all_end</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_File_write_ordered.3.html">17.2.155. MPI_File_write_ordered</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_Ineighbor_alltoall.3.html">17.2.214. MPI_Ineighbor_alltoall</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Ineighbor_alltoallv.3.html">17.2.215. MPI_Ineighbor_alltoallv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Ineighbor_alltoallw.3.html">17.2.216. MPI_Ineighbor_alltoallw</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_c2f.3.html">17.2.217. MPI_Info_c2f</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_create.3.html">17.2.218. MPI_Info_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_create_env.3.html">17.2.219. MPI_Info_create_env</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_delete.3.html">17.2.220. MPI_Info_delete</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_dup.3.html">17.2.221. MPI_Info_dup</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_env.3.html">17.2.222. MPI_Info_env</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_f2c.3.html">17.2.223. MPI_Info_f2c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_free.3.html">17.2.224. MPI_Info_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_get.3.html">17.2.225. MPI_Info_get</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_get_nkeys.3.html">17.2.226. MPI_Info_get_nkeys</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_get_nthkey.3.html">17.2.227. MPI_Info_get_nthkey</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_get_string.3.html">17.2.228. MPI_Info_get_string</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_get_valuelen.3.html">17.2.229. MPI_Info_get_valuelen</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Info_set.3.html">17.2.230. MPI_Info_set</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Init.3.html">17.2.231. MPI_Init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Init_thread.3.html">17.2.232. MPI_Init_thread</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Initialized.3.html">17.2.233. MPI_Initialized</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Intercomm_create.3.html">17.2.234. MPI_Intercomm_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Intercomm_create_from_groups.3.html">17.2.235. MPI_Intercomm_create_from_groups</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Intercomm_merge.3.html">17.2.236. MPI_Intercomm_merge</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Iprobe.3.html">17.2.237. MPI_Iprobe</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Irecv.3.html">17.2.238. MPI_Irecv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Ireduce.3.html">17.2.239. MPI_Ireduce</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Ireduce_scatter.3.html">17.2.240. MPI_Ireduce_scatter</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Ireduce_scatter_block.3.html">17.2.241. MPI_Ireduce_scatter_block</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Irsend.3.html">17.2.242. MPI_Irsend</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Is_thread_main.3.html">17.2.243. MPI_Is_thread_main</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Iscan.3.html">17.2.244. MPI_Iscan</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Iscatter.3.html">17.2.245. MPI_Iscatter</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Iscatterv.3.html">17.2.246. MPI_Iscatterv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Isend.3.html">17.2.247. MPI_Isend</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Isendrecv.3.html">17.2.248. MPI_Isendrecv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Isendrecv_replace.3.html">17.2.249. MPI_Isendrecv_replace</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Issend.3.html">17.2.250. MPI_Issend</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Keyval_create.3.html">17.2.251. MPI_Keyval_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Keyval_free.3.html">17.2.252. MPI_Keyval_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Lookup_name.3.html">17.2.253. MPI_Lookup_name</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Message_c2f.3.html">17.2.254. MPI_Message_c2f</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Message_f2c.3.html">17.2.255. MPI_Message_f2c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Mprobe.3.html">17.2.256. MPI_Mprobe</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Mrecv.3.html">17.2.257. MPI_Mrecv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_allgather.3.html">17.2.258. MPI_Neighbor_allgather</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_allgather_init.3.html">17.2.259. MPI_Neighbor_allgather_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_allgatherv.3.html">17.2.260. MPI_Neighbor_allgatherv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_allgatherv_init.3.html">17.2.261. MPI_Neighbor_allgatherv_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_alltoall.3.html">17.2.262. MPI_Neighbor_alltoall</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_alltoall_init.3.html">17.2.263. MPI_Neighbor_alltoall_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_alltoallv.3.html">17.2.264. MPI_Neighbor_alltoallv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_alltoallv_init.3.html">17.2.265. MPI_Neighbor_alltoallv_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_alltoallw.3.html">17.2.266. MPI_Neighbor_alltoallw</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Neighbor_alltoallw_init.3.html">17.2.267. MPI_Neighbor_alltoallw_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Op_c2f.3.html">17.2.268. MPI_Op_c2f</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Op_commutative.3.html">17.2.269. MPI_Op_commutative</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Op_create.3.html">17.2.270. MPI_Op_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Op_f2c.3.html">17.2.271. MPI_Op_f2c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Op_free.3.html">17.2.272. MPI_Op_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Open_port.3.html">17.2.273. MPI_Open_port</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pack.3.html">17.2.274. MPI_Pack</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pack_external.3.html">17.2.275. MPI_Pack_external</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pack_external_size.3.html">17.2.276. MPI_Pack_external_size</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pack_size.3.html">17.2.277. MPI_Pack_size</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Parrived.3.html">17.2.278. MPI_Parrived</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pcontrol.3.html">17.2.279. MPI_Pcontrol</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pready.3.html">17.2.280. MPI_Pready</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pready_list.3.html">17.2.281. MPI_Pready_list</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Pready_range.3.html">17.2.282. MPI_Pready_range</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Precv_init.3.html">17.2.283. MPI_Precv_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Probe.3.html">17.2.284. MPI_Probe</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Psend_init.3.html">17.2.285. MPI_Psend_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Publish_name.3.html">17.2.286. MPI_Publish_name</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Put.3.html">17.2.287. MPI_Put</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Query_thread.3.html">17.2.288. MPI_Query_thread</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Raccumulate.3.html">17.2.289. MPI_Raccumulate</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Recv.3.html">17.2.290. MPI_Recv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Recv_init.3.html">17.2.291. MPI_Recv_init</a></li>
<li class="toctree-l3 current"><a class="current reference internal" href="#">17.2.292. MPI_Reduce</a><ul>
<li class="toctree-l4"><a class="reference internal" href="#syntax">17.2.292.1. SYNTAX</a></li>
<li class="toctree-l4"><a class="reference internal" href="#input-parameters">17.2.292.2. INPUT PARAMETERS</a></li>
<li class="toctree-l4"><a class="reference internal" href="#output-parameters">17.2.292.3. OUTPUT PARAMETERS</a></li>
<li class="toctree-l4"><a class="reference internal" href="#description">17.2.292.4. DESCRIPTION</a></li>
<li class="toctree-l4"><a class="reference internal" href="#use-of-in-place-option">17.2.292.5. USE OF IN-PLACE OPTION</a></li>
<li class="toctree-l4"><a class="reference internal" href="#when-communicator-is-an-inter-communicator">17.2.292.6. WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR</a></li>
<li class="toctree-l4"><a class="reference internal" href="#predefined-reduce-operations">17.2.292.7. PREDEFINED REDUCE OPERATIONS</a></li>
<li class="toctree-l4"><a class="reference internal" href="#minloc-and-maxloc">17.2.292.8. MINLOC AND MAXLOC</a></li>
<li class="toctree-l4"><a class="reference internal" href="#notes-on-collective-operations">17.2.292.9. NOTES ON COLLECTIVE OPERATIONS</a></li>
<li class="toctree-l4"><a class="reference internal" href="#errors">17.2.292.10. ERRORS</a></li>
</ul>
</li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Reduce_init.3.html">17.2.293. MPI_Reduce_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Reduce_local.3.html">17.2.294. MPI_Reduce_local</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Reduce_scatter.3.html">17.2.295. MPI_Reduce_scatter</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Reduce_scatter_block.3.html">17.2.296. MPI_Reduce_scatter_block</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Reduce_scatter_block_init.3.html">17.2.297. MPI_Reduce_scatter_block_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Reduce_scatter_init.3.html">17.2.298. MPI_Reduce_scatter_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Register_datarep.3.html">17.2.299. MPI_Register_datarep</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Request_c2f.3.html">17.2.300. MPI_Request_c2f</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Request_f2c.3.html">17.2.301. MPI_Request_f2c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Request_free.3.html">17.2.302. MPI_Request_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Request_get_status.3.html">17.2.303. MPI_Request_get_status</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Rget.3.html">17.2.304. MPI_Rget</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Rget_accumulate.3.html">17.2.305. MPI_Rget_accumulate</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Rput.3.html">17.2.306. MPI_Rput</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Rsend.3.html">17.2.307. MPI_Rsend</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Rsend_init.3.html">17.2.308. MPI_Rsend_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Scan.3.html">17.2.309. MPI_Scan</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Scan_init.3.html">17.2.310. MPI_Scan_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Scatter.3.html">17.2.311. MPI_Scatter</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Scatter_init.3.html">17.2.312. MPI_Scatter_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Scatterv.3.html">17.2.313. MPI_Scatterv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Scatterv_init.3.html">17.2.314. MPI_Scatterv_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Send.3.html">17.2.315. MPI_Send</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Send_init.3.html">17.2.316. MPI_Send_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Sendrecv.3.html">17.2.317. MPI_Sendrecv</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Sendrecv_replace.3.html">17.2.318. MPI_Sendrecv_replace</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_call_errhandler.3.html">17.2.319. MPI_Session_call_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_create_errhandler.3.html">17.2.320. MPI_Session_create_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_f2c.3.html">17.2.321. MPI_Session_f2c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_finalize.3.html">17.2.322. MPI_Session_finalize</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_get_errhandler.3.html">17.2.323. MPI_Session_get_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_get_info.3.html">17.2.324. MPI_Session_get_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_get_nth_pset.3.html">17.2.325. MPI_Session_get_nth_pset</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_get_num_psets.3.html">17.2.326. MPI_Session_get_num_psets</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_get_pset_info.3.html">17.2.327. MPI_Session_get_pset_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_init.3.html">17.2.328. MPI_Session_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Session_set_errhandler.3.html">17.2.329. MPI_Session_set_errhandler</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Sizeof.3.html">17.2.330. MPI_Sizeof</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Ssend.3.html">17.2.331. MPI_Ssend</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Ssend_init.3.html">17.2.332. MPI_Ssend_init</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Start.3.html">17.2.333. MPI_Start</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Startall.3.html">17.2.334. MPI_Startall</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_c2f.3.html">17.2.335. MPI_Status_c2f</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_c2f08.3.html">17.2.336. MPI_Status_c2f08</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_f082c.3.html">17.2.337. MPI_Status_f082c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_f082f.3.html">17.2.338. MPI_Status_f082f</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_f2c.3.html">17.2.339. MPI_Status_f2c</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_f2f08.3.html">17.2.340. MPI_Status_f2f08</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_set_cancelled.3.html">17.2.341. MPI_Status_set_cancelled</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_set_elements.3.html">17.2.342. MPI_Status_set_elements</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Status_set_elements_x.3.html">17.2.343. MPI_Status_set_elements_x</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T.3.html">17.2.344. MPI_T</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_category_changed.3.html">17.2.345. MPI_T_category_changed</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_category_get_categories.3.html">17.2.346. MPI_T_category_get_categories</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_category_get_cvars.3.html">17.2.347. MPI_T_category_get_cvars</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_category_get_info.3.html">17.2.348. MPI_T_category_get_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_category_get_num.3.html">17.2.349. MPI_T_category_get_num</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_category_get_pvars.3.html">17.2.350. MPI_T_category_get_pvars</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_cvar_get_info.3.html">17.2.351. MPI_T_cvar_get_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_cvar_get_num.3.html">17.2.352. MPI_T_cvar_get_num</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_cvar_handle_alloc.3.html">17.2.353. MPI_T_cvar_handle_alloc</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_cvar_handle_free.3.html">17.2.354. MPI_T_cvar_handle_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_cvar_read.3.html">17.2.355. MPI_T_cvar_read</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_cvar_write.3.html">17.2.356. MPI_T_cvar_write</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_enum_get_info.3.html">17.2.357. MPI_T_enum_get_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_enum_get_item.3.html">17.2.358. MPI_T_enum_get_item</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_finalize.3.html">17.2.359. MPI_T_finalize</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_init_thread.3.html">17.2.360. MPI_T_init_thread</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_get_info.3.html">17.2.361. MPI_T_pvar_get_info</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_get_num.3.html">17.2.362. MPI_T_pvar_get_num</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_handle_alloc.3.html">17.2.363. MPI_T_pvar_handle_alloc</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_handle_free.3.html">17.2.364. MPI_T_pvar_handle_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_read.3.html">17.2.365. MPI_T_pvar_read</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_reset.3.html">17.2.367. MPI_T_pvar_reset</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_session_create.3.html">17.2.368. MPI_T_pvar_session_create</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_session_free.3.html">17.2.369. MPI_T_pvar_session_free</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_start.3.html">17.2.370. MPI_T_pvar_start</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_stop.3.html">17.2.371. MPI_T_pvar_stop</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_T_pvar_write.3.html">17.2.372. MPI_T_pvar_write</a></li>
<li class="toctree-l3"><a class="reference internal" href="MPI_Test.3.html">17.2.373. MPI_Test</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_Testall.3.html">17.2.375. MPI_Testall</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_Type_c2f.3.html">17.2.379. MPI_Type_c2f</a></li>
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<li class="toctree-l3"><a class="reference internal" href="MPI_Type_create_f90_integer.3.html">17.2.384. MPI_Type_create_f90_integer</a></li>
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<span id="id1"></span><h1><span class="section-number">17.2.292. </span>MPI_Reduce<a class="headerlink" href="#mpi-reduce" title="Permalink to this heading"></a></h1>
<p><a class="reference internal" href="#mpi-reduce"><span class="std std-ref">MPI_Reduce</span></a>, <a class="reference internal" href="MPI_Ireduce.3.html#mpi-ireduce"><span class="std std-ref">MPI_Ireduce</span></a>, <a class="reference internal" href="MPI_Reduce_init.3.html#mpi-reduce-init"><span class="std std-ref">MPI_Reduce_init</span></a> - Reduces values on all
processes within a group.</p>
<div class="section" id="syntax">
<h2><span class="section-number">17.2.292.1. </span>SYNTAX<a class="headerlink" href="#syntax" title="Permalink to this heading"></a></h2>
<div class="section" id="c-syntax">
<h3><span class="section-number">17.2.292.1.1. </span>C Syntax<a class="headerlink" href="#c-syntax" title="Permalink to this heading"></a></h3>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><mpi.h></span>
<span class="kt">int</span><span class="w"> </span><span class="n">MPI_Reduce</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">sendbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">recvbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_Datatype</span><span class="w"> </span><span class="n">datatype</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_Op</span><span class="w"> </span><span class="n">op</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">root</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_Comm</span><span class="w"> </span><span class="n">comm</span><span class="p">)</span>
<span class="kt">int</span><span class="w"> </span><span class="n">MPI_Ireduce</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">sendbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">recvbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_Datatype</span><span class="w"> </span><span class="n">datatype</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_Op</span><span class="w"> </span><span class="n">op</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">root</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_Comm</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_Request</span><span class="w"> </span><span class="o">*</span><span class="n">request</span><span class="p">)</span>
<span class="kt">int</span><span class="w"> </span><span class="n">MPI_Reduce_init</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">sendbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">recvbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_Datatype</span><span class="w"> </span><span class="n">datatype</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_Op</span><span class="w"> </span><span class="n">op</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">root</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_Comm</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_Info</span><span class="w"> </span><span class="n">info</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_Request</span><span class="w"> </span><span class="o">*</span><span class="n">request</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="fortran-syntax">
<h3><span class="section-number">17.2.292.1.2. </span>Fortran Syntax<a class="headerlink" href="#fortran-syntax" title="Permalink to this heading"></a></h3>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">USE </span><span class="n">MPI</span>
<span class="c">! or the older form: INCLUDE 'mpif.h'</span>
<span class="n">MPI_REDUCE</span><span class="p">(</span><span class="n">SENDBUF</span><span class="p">,</span><span class="w"> </span><span class="n">RECVBUF</span><span class="p">,</span><span class="w"> </span><span class="nb">COUNT</span><span class="p">,</span><span class="w"> </span><span class="n">DATATYPE</span><span class="p">,</span><span class="w"> </span><span class="n">OP</span><span class="p">,</span><span class="w"> </span><span class="n">ROOT</span><span class="p">,</span><span class="w"> </span><span class="n">COMM</span><span class="p">,</span>
<span class="w"> </span><span class="n">IERROR</span><span class="p">)</span>
<span class="w"> </span><span class="o"><</span><span class="k">type</span><span class="o">></span><span class="w"> </span><span class="n">SENDBUF</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="n">RECVBUF</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>
<span class="w"> </span><span class="kt">INTEGER </span><span class="nb">COUNT</span><span class="p">,</span><span class="w"> </span><span class="n">DATATYPE</span><span class="p">,</span><span class="w"> </span><span class="n">OP</span><span class="p">,</span><span class="w"> </span><span class="n">ROOT</span><span class="p">,</span><span class="w"> </span><span class="n">COMM</span><span class="p">,</span><span class="w"> </span><span class="n">IERROR</span>
<span class="n">MPI_IREDUCE</span><span class="p">(</span><span class="n">SENDBUF</span><span class="p">,</span><span class="w"> </span><span class="n">RECVBUF</span><span class="p">,</span><span class="w"> </span><span class="nb">COUNT</span><span class="p">,</span><span class="w"> </span><span class="n">DATATYPE</span><span class="p">,</span><span class="w"> </span><span class="n">OP</span><span class="p">,</span><span class="w"> </span><span class="n">ROOT</span><span class="p">,</span><span class="w"> </span><span class="n">COMM</span><span class="p">,</span>
<span class="w"> </span><span class="n">REQUEST</span><span class="p">,</span><span class="w"> </span><span class="n">IERROR</span><span class="p">)</span>
<span class="w"> </span><span class="o"><</span><span class="k">type</span><span class="o">></span><span class="w"> </span><span class="n">SENDBUF</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="n">RECVBUF</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>
<span class="w"> </span><span class="kt">INTEGER </span><span class="nb">COUNT</span><span class="p">,</span><span class="w"> </span><span class="n">DATATYPE</span><span class="p">,</span><span class="w"> </span><span class="n">OP</span><span class="p">,</span><span class="w"> </span><span class="n">ROOT</span><span class="p">,</span><span class="w"> </span><span class="n">COMM</span><span class="p">,</span><span class="w"> </span><span class="n">REQUEST</span><span class="p">,</span><span class="w"> </span><span class="n">IERROR</span>
<span class="n">MPI_REDUCE_INIT</span><span class="p">(</span><span class="n">SENDBUF</span><span class="p">,</span><span class="w"> </span><span class="n">RECVBUF</span><span class="p">,</span><span class="w"> </span><span class="nb">COUNT</span><span class="p">,</span><span class="w"> </span><span class="n">DATATYPE</span><span class="p">,</span><span class="w"> </span><span class="n">OP</span><span class="p">,</span><span class="w"> </span><span class="n">ROOT</span><span class="p">,</span><span class="w"> </span><span class="n">COMM</span><span class="p">,</span>
<span class="w"> </span><span class="n">INFO</span><span class="p">,</span><span class="w"> </span><span class="n">REQUEST</span><span class="p">,</span><span class="w"> </span><span class="n">IERROR</span><span class="p">)</span>
<span class="w"> </span><span class="o"><</span><span class="k">type</span><span class="o">></span><span class="w"> </span><span class="n">SENDBUF</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="n">RECVBUF</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>
<span class="w"> </span><span class="kt">INTEGER </span><span class="nb">COUNT</span><span class="p">,</span><span class="w"> </span><span class="n">DATATYPE</span><span class="p">,</span><span class="w"> </span><span class="n">OP</span><span class="p">,</span><span class="w"> </span><span class="n">ROOT</span><span class="p">,</span><span class="w"> </span><span class="n">COMM</span><span class="p">,</span><span class="w"> </span><span class="n">INFO</span><span class="p">,</span><span class="w"> </span><span class="n">REQUEST</span><span class="p">,</span><span class="w"> </span><span class="n">IERROR</span>
</pre></div>
</div>
</div>
<div class="section" id="fortran-2008-syntax">
<h3><span class="section-number">17.2.292.1.3. </span>Fortran 2008 Syntax<a class="headerlink" href="#fortran-2008-syntax" title="Permalink to this heading"></a></h3>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">USE </span><span class="n">mpi_f08</span>
<span class="n">MPI_Reduce</span><span class="p">(</span><span class="n">sendbuf</span><span class="p">,</span><span class="w"> </span><span class="n">recvbuf</span><span class="p">,</span><span class="w"> </span><span class="nb">count</span><span class="p">,</span><span class="w"> </span><span class="n">datatype</span><span class="p">,</span><span class="w"> </span><span class="n">op</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">ierror</span><span class="p">)</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="k">DIMENSION</span><span class="p">(..),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">sendbuf</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="k">DIMENSION</span><span class="p">(..)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">recvbuf</span>
<span class="w"> </span><span class="kt">INTEGER</span><span class="p">,</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="nb">count</span><span class="p">,</span><span class="w"> </span><span class="n">root</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Datatype</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">datatype</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Op</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">op</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Comm</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">comm</span>
<span class="w"> </span><span class="kt">INTEGER</span><span class="p">,</span><span class="w"> </span><span class="k">OPTIONAL</span><span class="p">,</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">OUT</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">ierror</span>
<span class="n">MPI_Ireduce</span><span class="p">(</span><span class="n">sendbuf</span><span class="p">,</span><span class="w"> </span><span class="n">recvbuf</span><span class="p">,</span><span class="w"> </span><span class="nb">count</span><span class="p">,</span><span class="w"> </span><span class="n">datatype</span><span class="p">,</span><span class="w"> </span><span class="n">op</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">request</span><span class="p">,</span>
<span class="w"> </span><span class="n">ierror</span><span class="p">)</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="k">DIMENSION</span><span class="p">(..),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">),</span><span class="w"> </span><span class="k">ASYNCHRONOUS</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">sendbuf</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="k">DIMENSION</span><span class="p">(..),</span><span class="w"> </span><span class="k">ASYNCHRONOUS</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">recvbuf</span>
<span class="w"> </span><span class="kt">INTEGER</span><span class="p">,</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="nb">count</span><span class="p">,</span><span class="w"> </span><span class="n">root</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Datatype</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">datatype</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Op</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">op</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Comm</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">comm</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Request</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">OUT</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">request</span>
<span class="w"> </span><span class="kt">INTEGER</span><span class="p">,</span><span class="w"> </span><span class="k">OPTIONAL</span><span class="p">,</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">OUT</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">ierror</span>
<span class="n">MPI_Reduce_init</span><span class="p">(</span><span class="n">sendbuf</span><span class="p">,</span><span class="w"> </span><span class="n">recvbuf</span><span class="p">,</span><span class="w"> </span><span class="nb">count</span><span class="p">,</span><span class="w"> </span><span class="n">datatype</span><span class="p">,</span><span class="w"> </span><span class="n">op</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">info</span><span class="p">,</span><span class="w"> </span><span class="n">request</span><span class="p">,</span>
<span class="w"> </span><span class="n">ierror</span><span class="p">)</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="k">DIMENSION</span><span class="p">(..),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">),</span><span class="w"> </span><span class="k">ASYNCHRONOUS</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">sendbuf</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="o">*</span><span class="p">),</span><span class="w"> </span><span class="k">DIMENSION</span><span class="p">(..),</span><span class="w"> </span><span class="k">ASYNCHRONOUS</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">recvbuf</span>
<span class="w"> </span><span class="kt">INTEGER</span><span class="p">,</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="nb">count</span><span class="p">,</span><span class="w"> </span><span class="n">root</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Datatype</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">datatype</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Op</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">op</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Comm</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">comm</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Info</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">IN</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">info</span>
<span class="w"> </span><span class="k">TYPE</span><span class="p">(</span><span class="n">MPI_Request</span><span class="p">),</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">OUT</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">request</span>
<span class="w"> </span><span class="kt">INTEGER</span><span class="p">,</span><span class="w"> </span><span class="k">OPTIONAL</span><span class="p">,</span><span class="w"> </span><span class="k">INTENT</span><span class="p">(</span><span class="n">OUT</span><span class="p">)</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">ierror</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="input-parameters">
<h2><span class="section-number">17.2.292.2. </span>INPUT PARAMETERS<a class="headerlink" href="#input-parameters" title="Permalink to this heading"></a></h2>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">sendbuf</span></code>: Address of send buffer (choice).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">count</span></code>: Number of elements in send buffer (integer).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">datatype</span></code>: Data type of elements of send buffer (handle).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">op</span></code>: Reduce operation (handle).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">root</span></code>: Rank of root process (integer).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">comm</span></code>: Communicator (handle).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">info</span></code>: Info (handle, persistent).</p></li>
</ul>
</div>
<div class="section" id="output-parameters">
<h2><span class="section-number">17.2.292.3. </span>OUTPUT PARAMETERS<a class="headerlink" href="#output-parameters" title="Permalink to this heading"></a></h2>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">recvbuf</span></code>: Address of receive buffer (choice, significant only at root).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">request</span></code>: Request (handle, non-blocking only).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">ierror</span></code>: Fortran only: Error status (integer).</p></li>
</ul>
</div>
<div class="section" id="description">
<h2><span class="section-number">17.2.292.4. </span>DESCRIPTION<a class="headerlink" href="#description" title="Permalink to this heading"></a></h2>
<p>The global reduce functions (<a class="reference internal" href="#mpi-reduce"><span class="std std-ref">MPI_Reduce</span></a>, <a class="reference internal" href="MPI_Op_create.3.html#mpi-op-create"><span class="std std-ref">MPI_Op_create</span></a>, <a class="reference internal" href="MPI_Op_free.3.html#mpi-op-free"><span class="std std-ref">MPI_Op_free</span></a>,
<a class="reference internal" href="MPI_Allreduce.3.html#mpi-allreduce"><span class="std std-ref">MPI_Allreduce</span></a>, <a class="reference internal" href="MPI_Reduce_scatter.3.html#mpi-reduce-scatter"><span class="std std-ref">MPI_Reduce_scatter</span></a>, MPI_Scan) perform a global reduce
operation (such as sum, max, logical AND, etc.) across all the members
of a group. The reduction operation can be either one of a predefined
list of operations, or a user-defined operation. The global reduction
functions come in several flavors: a reduce that returns the result of
the reduction at one node, an all-reduce that returns this result at all
nodes, and a scan (parallel prefix) operation. In addition, a
reduce-scatter operation combines the functionality of a reduce and a
scatter operation.</p>
<p><a class="reference internal" href="#mpi-reduce"><span class="std std-ref">MPI_Reduce</span></a> combines the elements provided in the input buffer of each
process in the group, using the operation op, and returns the combined
value in the output buffer of the process with rank root. The input
buffer is defined by the arguments sendbuf, count, and datatype; the
output buffer is defined by the arguments recvbuf, count, and datatype;
both have the same number of elements, with the same type. The routine
is called by all group members using the same arguments for count,
datatype, op, root, and comm. Thus, all processes provide input buffers
and output buffers of the same length, with elements of the same type.
Each process can provide one element, or a sequence of elements, in
which case the combine operation is executed element-wise on each entry
of the sequence. For example, if the operation is MPI_MAX and the send
buffer contains two elements that are floating-point numbers (count = 2
and datatype = MPI_FLOAT), then recvbuf(1) = global max (sendbuf(1)) and
recvbuf(2) = global max(sendbuf(2)).</p>
</div>
<div class="section" id="use-of-in-place-option">
<h2><span class="section-number">17.2.292.5. </span>USE OF IN-PLACE OPTION<a class="headerlink" href="#use-of-in-place-option" title="Permalink to this heading"></a></h2>
<p>When the communicator is an intracommunicator, you can perform a reduce
operation in-place (the output buffer is used as the input buffer). Use
the variable MPI_IN_PLACE as the value of the root process <em>sendbuf</em>. In
this case, the input data is taken at the root from the receive buffer,
where it will be replaced by the output data.</p>
<p>Note that MPI_IN_PLACE is a special kind of value; it has the same
restrictions on its use as MPI_BOTTOM.</p>
<p>Because the in-place option converts the receive buffer into a
send-and-receive buffer, a Fortran binding that includes INTENT must
mark these as INOUT, not OUT.</p>
</div>
<div class="section" id="when-communicator-is-an-inter-communicator">
<h2><span class="section-number">17.2.292.6. </span>WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR<a class="headerlink" href="#when-communicator-is-an-inter-communicator" title="Permalink to this heading"></a></h2>
<p>When the communicator is an inter-communicator, the root process in the
first group combines data from all the processes in the second group and
then performs the <em>op</em> operation. The first group defines the root
process. That process uses MPI_ROOT as the value of its <em>root</em> argument.
The remaining processes use <code class="docutils literal notranslate"><span class="pre">MPI_PROC_NULL</span></code> as the value of their <em>root</em>
argument. All processes in the second group use the rank of that root
process in the first group as the value of their <em>root</em> argument. Only
the send buffer arguments are significant in the second group, and only
the receive buffer arguments are significant in the root process of the
first group.</p>
</div>
<div class="section" id="predefined-reduce-operations">
<h2><span class="section-number">17.2.292.7. </span>PREDEFINED REDUCE OPERATIONS<a class="headerlink" href="#predefined-reduce-operations" title="Permalink to this heading"></a></h2>
<p>The set of predefined operations provided by MPI is listed below
(Predefined Reduce Operations). That section also enumerates the
datatypes each operation can be applied to. In addition, users may
define their own operations that can be overloaded to operate on several
datatypes, either basic or derived. This is further explained in the
description of the user-defined operations (see the man pages for
<a class="reference internal" href="MPI_Op_create.3.html#mpi-op-create"><span class="std std-ref">MPI_Op_create</span></a> and MPI_Op_free).</p>
<p>The operation op is always assumed to be associative. All predefined
operations are also assumed to be commutative. Users may define
operations that are assumed to be associative, but not commutative. The
``canonical’’ evaluation order of a reduction is determined by the
ranks of the processes in the group. However, the implementation can
take advantage of associativity, or associativity and commutativity, in
order to change the order of evaluation. This may change the result of
the reduction for operations that are not strictly associative and
commutative, such as floating point addition.</p>
<p>Predefined operators work only with the MPI types listed below
(Predefined Reduce Operations, and the section MINLOC and MAXLOC,
below). User-defined operators may operate on general, derived
datatypes. In this case, each argument that the reduce operation is
applied to is one element described by such a datatype, which may
contain several basic values. This is further explained in Section 4.9.4
of the MPI Standard, “User-Defined Operations.”</p>
<p>The following predefined operations are supplied for <a class="reference internal" href="#mpi-reduce"><span class="std std-ref">MPI_Reduce</span></a> and
related functions <a class="reference internal" href="MPI_Allreduce.3.html#mpi-allreduce"><span class="std std-ref">MPI_Allreduce</span></a>, <a class="reference internal" href="MPI_Reduce_scatter.3.html#mpi-reduce-scatter"><span class="std std-ref">MPI_Reduce_scatter</span></a>, and <a class="reference internal" href="MPI_Scan.3.html#mpi-scan"><span class="std std-ref">MPI_Scan</span></a>. These
operations are invoked by placing the following in op:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>Name Meaning
--------- --------------------
MPI_MAX maximum
MPI_MIN minimum
MPI_SUM sum
MPI_PROD product
MPI_LAND logical and
MPI_BAND bit-wise and
MPI_LOR logical or
MPI_BOR bit-wise or
MPI_LXOR logical xor
MPI_BXOR bit-wise xor
MPI_MAXLOC max value and location
MPI_MINLOC min value and location
</pre></div>
</div>
<p>The two operations MPI_MINLOC and MPI_MAXLOC are discussed separately
below (MINLOC and MAXLOC). For the other predefined operations, we
enumerate below the allowed combinations of op and datatype arguments.
First, define groups of MPI basic datatypes in the following way:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">C</span><span class="w"> </span><span class="n">integer</span><span class="o">:</span><span class="w"> </span><span class="n">MPI_INT</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_LONG</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_SHORT</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_UNSIGNED_SHORT</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_UNSIGNED</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_UNSIGNED_LONG</span>
<span class="n">Fortran</span><span class="w"> </span><span class="n">integer</span><span class="o">:</span><span class="w"> </span><span class="n">MPI_INTEGER</span>
<span class="n">Floating</span><span class="o">-</span><span class="n">point</span><span class="o">:</span><span class="w"> </span><span class="n">MPI_FLOAT</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_DOUBLE</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_REAL</span><span class="p">,</span>
<span class="w"> </span><span class="n">MPI_DOUBLE_PRECISION</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_LONG_DOUBLE</span>
<span class="nl">Logical</span><span class="p">:</span><span class="w"> </span><span class="n">MPI_LOGICAL</span>
<span class="nl">Complex</span><span class="p">:</span><span class="w"> </span><span class="n">MPI_COMPLEX</span>
<span class="nl">Byte</span><span class="p">:</span><span class="w"> </span><span class="n">MPI_BYTE</span>
</pre></div>
</div>
<p>Now, the valid datatypes for each option is specified below.</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>Op Allowed Types
---------------- ---------------------------
MPI_MAX, MPI_MIN C integer, Fortran integer,
floating-point
MPI_SUM, MPI_PROD C integer, Fortran integer,
floating-point, complex
MPI_LAND, MPI_LOR, C integer, logical
MPI_LXOR
MPI_BAND, MPI_BOR, C integer, Fortran integer, byte
MPI_BXOR
</pre></div>
</div>
<p><strong>Example 1:</strong> A routine that computes the dot product of two vectors
that are distributed across a group of processes and returns the answer
at process zero.</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">SUBROUTINE </span><span class="n">PAR_BLAS1</span><span class="p">(</span><span class="n">m</span><span class="p">,</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="n">c</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">)</span>
<span class="kt">REAL </span><span class="n">a</span><span class="p">(</span><span class="n">m</span><span class="p">),</span><span class="w"> </span><span class="n">b</span><span class="p">(</span><span class="n">m</span><span class="p">)</span><span class="w"> </span><span class="c">! local slice of array</span>
<span class="kt">REAL </span><span class="n">c</span><span class="w"> </span><span class="c">! result (at process zero)</span>
<span class="kt">REAL </span><span class="nb">sum</span>
<span class="kt">INTEGER </span><span class="n">m</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span>
<span class="c">! local sum</span>
<span class="nb">sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">0.0</span>
<span class="k">DO </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">m</span>
<span class="w"> </span><span class="nb">sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">a</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="o">*</span><span class="n">b</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
<span class="k">END DO</span>
<span class="c">! global sum</span>
<span class="k">CALL </span><span class="n">MPI_REDUCE</span><span class="p">(</span><span class="nb">sum</span><span class="p">,</span><span class="w"> </span><span class="n">c</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_REAL</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_SUM</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="k">RETURN</span>
</pre></div>
</div>
<p><strong>Example 2:</strong> A routine that computes the product of a vector and an
array that are distributed across a group of processes and returns the
answer at process zero.</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">SUBROUTINE </span><span class="n">PAR_BLAS2</span><span class="p">(</span><span class="n">m</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="n">c</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">)</span>
<span class="kt">REAL </span><span class="n">a</span><span class="p">(</span><span class="n">m</span><span class="p">),</span><span class="w"> </span><span class="n">b</span><span class="p">(</span><span class="n">m</span><span class="p">,</span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="c">! local slice of array</span>
<span class="kt">REAL </span><span class="n">c</span><span class="p">(</span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="c">! result</span>
<span class="kt">REAL </span><span class="nb">sum</span><span class="p">(</span><span class="n">n</span><span class="p">)</span>
<span class="kt">INTEGER </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">j</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span>
<span class="c">! local sum</span>
<span class="k">DO </span><span class="n">j</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">n</span>
<span class="w"> </span><span class="nb">sum</span><span class="p">(</span><span class="n">j</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">0.0</span>
<span class="w"> </span><span class="k">DO </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">m</span>
<span class="w"> </span><span class="nb">sum</span><span class="p">(</span><span class="n">j</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">sum</span><span class="p">(</span><span class="n">j</span><span class="p">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">a</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="o">*</span><span class="n">b</span><span class="p">(</span><span class="n">i</span><span class="p">,</span><span class="n">j</span><span class="p">)</span>
<span class="w"> </span><span class="k">END DO</span>
<span class="k">END DO</span>
<span class="c">! global sum</span>
<span class="k">CALL </span><span class="n">MPI_REDUCE</span><span class="p">(</span><span class="nb">sum</span><span class="p">,</span><span class="w"> </span><span class="n">c</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_REAL</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_SUM</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="c">! return result at process zero (and garbage at the other nodes)</span>
<span class="k">RETURN</span>
</pre></div>
</div>
</div>
<div class="section" id="minloc-and-maxloc">
<h2><span class="section-number">17.2.292.8. </span>MINLOC AND MAXLOC<a class="headerlink" href="#minloc-and-maxloc" title="Permalink to this heading"></a></h2>
<p>The operator MPI_MINLOC is used to compute a global minimum and also an
index attached to the minimum value. MPI_MAXLOC similarly computes a
global maximum and index. One application of these is to compute a
global minimum (maximum) and the rank of the process containing this
value.</p>
<p>The operation that defines MPI_MAXLOC is</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span> ( u ) ( v ) ( w )
( ) o ( ) = ( )
( i ) ( j ) ( k )
where
w = max(u, v)
and
( i if u > v
(
k = ( min(i, j) if u = v
(
( j if u < v)
</pre></div>
</div>
<p>MPI_MINLOC is defined similarly:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span> ( u ) ( v ) ( w )
( ) o ( ) = ( )
( i ) ( j ) ( k )
where
w = min(u, v)
and
( i if u < v
(
k = ( min(i, j) if u = v
(
( j if u > v)
</pre></div>
</div>
<p>Both operations are associative and commutative. Note that if MPI_MAXLOC
is applied to reduce a sequence of pairs (u(0), 0), (u(1), 1), …,
(u(n-1), n-1), then the value returned is (u , r), where u= max(i) u(i)
and r is the index of the first global maximum in the sequence. Thus, if
each process supplies a value and its rank within the group, then a
reduce operation with op = MPI_MAXLOC will return the maximum value and
the rank of the first process with that value. Similarly, MPI_MINLOC can
be used to return a minimum and its index. More generally, MPI_MINLOC
computes a lexicographic minimum, where elements are ordered according
to the first component of each pair, and ties are resolved according to
the second component.</p>
<p>The reduce operation is defined to operate on arguments that consist of
a pair: value and index. For both Fortran and C, types are provided to
describe the pair. The potentially mixed-type nature of such arguments
is a problem in Fortran. The problem is circumvented, for Fortran, by
having the MPI-provided type consist of a pair of the same type as
value, and coercing the index to this type also. In C, the MPI-provided
pair type has distinct types and the index is an int.</p>
<p>In order to use MPI_MINLOC and MPI_MAXLOC in a reduce operation, one
must provide a datatype argument that represents a pair (value and
index). MPI provides nine such predefined datatypes. The operations
MPI_MAXLOC and MPI_MINLOC can be used with each of the following
datatypes:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>Fortran:
Name Description
MPI_2REAL pair of REALs
MPI_2DOUBLE_PRECISION pair of DOUBLE-PRECISION variables
MPI_2INTEGER pair of INTEGERs
C:
Name Description
MPI_FLOAT_INT float and int
MPI_DOUBLE_INT double and int
MPI_LONG_INT long and int
MPI_2INT pair of ints
MPI_SHORT_INT short and int
MPI_LONG_DOUBLE_INT long double and int
</pre></div>
</div>
<p>The data type MPI_2REAL is equivalent to:</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n">MPI_TYPE_CONTIGUOUS</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_REAL</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_2REAL</span><span class="p">)</span>
</pre></div>
</div>
<p>Similar statements apply for MPI_2INTEGER, MPI_2DOUBLE_PRECISION, and
MPI_2INT.</p>
<p>The datatype MPI_FLOAT_INT is as if defined by the following sequence of
instructions.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">type</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MPI_FLOAT</span>
<span class="n">type</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MPI_INT</span>
<span class="n">disp</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span>
<span class="n">disp</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">float</span><span class="p">)</span>
<span class="n">block</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span>
<span class="n">block</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span>
<span class="n">MPI_TYPE_STRUCT</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">block</span><span class="p">,</span><span class="w"> </span><span class="n">disp</span><span class="p">,</span><span class="w"> </span><span class="n">type</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_FLOAT_INT</span><span class="p">)</span>
</pre></div>
</div>
<p>Similar statements apply for MPI_LONG_INT and MPI_DOUBLE_INT.</p>
<p><strong>Example 3:</strong> Each process has an array of 30 doubles, in C. For each
of the 30 locations, compute the value and rank of the process
containing the largest value.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="p">...</span>
<span class="cm">/* each process has an array of 30 double: ain[30]</span>
<span class="cm"> */</span>
<span class="kt">double</span><span class="w"> </span><span class="n">ain</span><span class="p">[</span><span class="mi">30</span><span class="p">],</span><span class="w"> </span><span class="n">aout</span><span class="p">[</span><span class="mi">30</span><span class="p">];</span>
<span class="kt">int</span><span class="w"> </span><span class="n">ind</span><span class="p">[</span><span class="mi">30</span><span class="p">];</span>
<span class="k">struct</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">val</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rank</span><span class="p">;</span>
<span class="p">}</span><span class="w"> </span><span class="n">in</span><span class="p">[</span><span class="mi">30</span><span class="p">],</span><span class="w"> </span><span class="n">out</span><span class="p">[</span><span class="mi">30</span><span class="p">];</span>
<span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">myrank</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">;</span>
<span class="n">MPI_Comm_rank</span><span class="p">(</span><span class="n">MPI_COMM_WORLD</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">myrank</span><span class="p">);</span>
<span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o"><</span><span class="mi">30</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">in</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ain</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<span class="w"> </span><span class="n">in</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">rank</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">myrank</span><span class="p">;</span>
<span class="p">}</span>
<span class="n">MPI_Reduce</span><span class="p">(</span><span class="w"> </span><span class="n">in</span><span class="p">,</span><span class="w"> </span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_DOUBLE_INT</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_MAXLOC</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="w"> </span><span class="p">);</span>
<span class="cm">/* At this point, the answer resides on process root</span>
<span class="cm"> */</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">myrank</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">root</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="cm">/* read ranks out</span>
<span class="cm"> */</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o"><</span><span class="mi">30</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">aout</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">out</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">val</span><span class="p">;</span>
<span class="w"> </span><span class="n">ind</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">out</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">rank</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
<p><strong>Example 4:</strong> Same example, in Fortran.</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="p">...</span>
<span class="c">! each process has an array of 30 double: ain(30)</span>
<span class="kt">DOUBLE PRECISION</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">ain</span><span class="p">(</span><span class="mi">30</span><span class="p">),</span><span class="w"> </span><span class="n">aout</span><span class="p">(</span><span class="mi">30</span><span class="p">)</span>
<span class="kt">INTEGER</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">ind</span><span class="p">(</span><span class="mi">30</span><span class="p">)</span>
<span class="kt">DOUBLE PRECISION</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">in</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">30</span><span class="p">),</span><span class="w"> </span><span class="n">out</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">30</span><span class="p">)</span>
<span class="kt">INTEGER</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">myrank</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span>
<span class="k">call </span><span class="n">MPI_COMM_RANK</span><span class="p">(</span><span class="n">MPI_COMM_WORLD</span><span class="p">,</span><span class="w"> </span><span class="n">myrank</span><span class="p">)</span>
<span class="k">DO </span><span class="n">I</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span>
<span class="w"> </span><span class="n">in</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ain</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
<span class="w"> </span><span class="n">in</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">myrank</span><span class="w"> </span><span class="c">! myrank is coerced to a double</span>
<span class="k">END DO</span>
<span class="k">call </span><span class="n">MPI_REDUCE</span><span class="p">(</span><span class="w"> </span><span class="n">in</span><span class="p">,</span><span class="w"> </span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_2DOUBLE_PRECISION</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_MAXLOC</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">,</span><span class="w"> </span><span class="p">&</span>
<span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="w"> </span><span class="p">)</span>
<span class="c">! At this point, the answer resides on process root</span>
<span class="k">IF</span><span class="w"> </span><span class="p">(</span><span class="n">myrank</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">root</span><span class="p">)</span><span class="w"> </span><span class="k">THEN</span>
<span class="w"> </span><span class="c">! read ranks out</span>
<span class="w"> </span><span class="k">DO </span><span class="n">I</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span>
<span class="w"> </span><span class="n">aout</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">out</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="n">i</span><span class="p">)</span>
<span class="w"> </span><span class="n">ind</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">out</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="c">! rank is coerced back to an integer</span>
<span class="w"> </span><span class="k">END DO</span>
<span class="k">END IF</span>
</pre></div>
</div>
<p><strong>Example 5:</strong> Each process has a nonempty array of values. Find the
minimum global value, the rank of the process that holds it, and its
index on this process.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define LEN 1000</span>
<span class="kt">float</span><span class="w"> </span><span class="n">val</span><span class="p">[</span><span class="n">LEN</span><span class="p">];</span><span class="w"> </span><span class="cm">/* local array of values */</span>
<span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">;</span><span class="w"> </span><span class="cm">/* local number of values */</span>
<span class="kt">int</span><span class="w"> </span><span class="n">myrank</span><span class="p">,</span><span class="w"> </span><span class="n">minrank</span><span class="p">,</span><span class="w"> </span><span class="n">minindex</span><span class="p">;</span>
<span class="kt">float</span><span class="w"> </span><span class="n">minval</span><span class="p">;</span>
<span class="k">struct</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">value</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">index</span><span class="p">;</span>
<span class="p">}</span><span class="w"> </span><span class="n">in</span><span class="p">,</span><span class="w"> </span><span class="n">out</span><span class="p">;</span>
<span class="cm">/* local minloc */</span>
<span class="n">in</span><span class="p">.</span><span class="n">value</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">val</span><span class="p">[</span><span class="mi">0</span><span class="p">];</span>
<span class="n">in</span><span class="p">.</span><span class="n">index</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="o">=</span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">count</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">in</span><span class="p">.</span><span class="n">value</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="n">val</span><span class="p">[</span><span class="n">i</span><span class="p">])</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">in</span><span class="p">.</span><span class="n">value</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">val</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<span class="w"> </span><span class="n">in</span><span class="p">.</span><span class="n">index</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="cm">/* global minloc */</span>
<span class="n">MPI_Comm_rank</span><span class="p">(</span><span class="n">MPI_COMM_WORLD</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">myrank</span><span class="p">);</span>
<span class="n">in</span><span class="p">.</span><span class="n">index</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">myrank</span><span class="o">*</span><span class="n">LEN</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">in</span><span class="p">.</span><span class="n">index</span><span class="p">;</span>
<span class="n">MPI_Reduce</span><span class="p">(</span><span class="w"> </span><span class="n">in</span><span class="p">,</span><span class="w"> </span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_FLOAT_INT</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_MINLOC</span><span class="p">,</span><span class="w"> </span><span class="n">root</span><span class="p">,</span><span class="w"> </span><span class="n">comm</span><span class="w"> </span><span class="p">);</span>
<span class="w"> </span><span class="cm">/* At this point, the answer resides on process root</span>
<span class="cm"> */</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">myrank</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">root</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="cm">/* read answer out</span>
<span class="cm"> */</span>
<span class="w"> </span><span class="n">minval</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">out</span><span class="p">.</span><span class="n">value</span><span class="p">;</span>
<span class="w"> </span><span class="n">minrank</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">out</span><span class="p">.</span><span class="n">index</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">LEN</span><span class="p">;</span>
<span class="w"> </span><span class="n">minindex</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">out</span><span class="p">.</span><span class="n">index</span><span class="w"> </span><span class="o">%</span><span class="w"> </span><span class="n">LEN</span><span class="p">;</span>
</pre></div>
</div>
<p>All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in
Fortran.</p>
</div>
<div class="section" id="notes-on-collective-operations">
<h2><span class="section-number">17.2.292.9. </span>NOTES ON COLLECTIVE OPERATIONS<a class="headerlink" href="#notes-on-collective-operations" title="Permalink to this heading"></a></h2>
<p>The reduction functions ( MPI_Op ) do not return an error value. As a
result, if the functions detect an error, all they can do is either call
<a class="reference internal" href="MPI_Abort.3.html#mpi-abort"><span class="std std-ref">MPI_Abort</span></a> or silently skip the problem. Thus, if you change the error
handler from MPI_ERRORS_ARE_FATAL to something else, for example,
MPI_ERRORS_RETURN , then no error may be indicated.</p>
<p>The reason for this is the performance problems in ensuring that all
collective routines return the same error value.</p>
</div>
<div class="section" id="errors">
<h2><span class="section-number">17.2.292.10. </span>ERRORS<a class="headerlink" href="#errors" title="Permalink to this heading"></a></h2>
<p>Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.</p>
<p>Before the error value is returned, the current MPI error handler associated
with the communication object (e.g., communicator, window, file) is called.
If no communication object is associated with the MPI call, then the call is
considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before
<a class="reference internal" href="MPI_Init.3.html#mpi-init"><span class="std std-ref">MPI_Init</span></a>/<a class="reference internal" href="MPI_Init_thread.3.html#mpi-init-thread"><span class="std std-ref">MPI_Init_thread</span></a>, after <a class="reference internal" href="MPI_Finalize.3.html#mpi-finalize"><span class="std std-ref">MPI_Finalize</span></a>, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling <a class="reference internal" href="MPI_Comm_set_errhandler.3.html#mpi-comm-set-errhandler"><span class="std std-ref">MPI_Comm_set_errhandler</span></a> on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to <a class="reference internal" href="MPI_Comm_spawn.3.html#mpi-comm-spawn"><span class="std std-ref">MPI_Comm_spawn</span></a>/<a class="reference internal" href="MPI_Comm_spawn_multiple.3.html#mpi-comm-spawn-multiple"><span class="std std-ref">MPI_Comm_spawn_multiple</span></a>.
If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
handler is called for all other MPI functions.</p>
<p>Open MPI includes three predefined error handlers that can be used:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">MPI_ERRORS_ARE_FATAL</span></code>
Causes the program to abort all connected MPI processes.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">MPI_ERRORS_ABORT</span></code>
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if <a class="reference internal" href="MPI_Abort.3.html#mpi-abort"><span class="std std-ref">MPI_Abort</span></a> was called on that communicator. If
called on a window or file, acts as if <a class="reference internal" href="MPI_Abort.3.html#mpi-abort"><span class="std std-ref">MPI_Abort</span></a> was called
on a communicator containing the group of processes in the
corresponding window or file. If called on a session,
aborts only the local process.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">MPI_ERRORS_RETURN</span></code>
Returns an error code to the application.</p></li>
</ul>
<p>MPI applications can also implement their own error handlers by calling:</p>
<ul class="simple">
<li><p><a class="reference internal" href="MPI_Comm_create_errhandler.3.html#mpi-comm-create-errhandler"><span class="std std-ref">MPI_Comm_create_errhandler</span></a> then <a class="reference internal" href="MPI_Comm_set_errhandler.3.html#mpi-comm-set-errhandler"><span class="std std-ref">MPI_Comm_set_errhandler</span></a></p></li>
<li><p><a class="reference internal" href="MPI_File_create_errhandler.3.html#mpi-file-create-errhandler"><span class="std std-ref">MPI_File_create_errhandler</span></a> then <a class="reference internal" href="MPI_File_set_errhandler.3.html#mpi-file-set-errhandler"><span class="std std-ref">MPI_File_set_errhandler</span></a></p></li>
<li><p><a class="reference internal" href="MPI_Session_create_errhandler.3.html#mpi-session-create-errhandler"><span class="std std-ref">MPI_Session_create_errhandler</span></a> then <a class="reference internal" href="MPI_Session_set_errhandler.3.html#mpi-session-set-errhandler"><span class="std std-ref">MPI_Session_set_errhandler</span></a> or at <a class="reference internal" href="MPI_Session_init.3.html#mpi-session-init"><span class="std std-ref">MPI_Session_init</span></a></p></li>
<li><p><a class="reference internal" href="MPI_Win_create_errhandler.3.html#mpi-win-create-errhandler"><span class="std std-ref">MPI_Win_create_errhandler</span></a> then <a class="reference internal" href="MPI_Win_set_errhandler.3.html#mpi-win-set-errhandler"><span class="std std-ref">MPI_Win_set_errhandler</span></a></p></li>
</ul>
<p>Note that MPI does not guarantee that an MPI program can continue past
an error.</p>
<p>See the <a class="reference internal" href="../man7/Open-MPI.7.html#open-mpi"><span class="std std-ref">MPI man page</span></a> for a full list of <a class="reference internal" href="MPI_Errors.3.html#open-mpi-errors"><span class="std std-ref">MPI error codes</span></a>.</p>
<p>See the Error Handling section of the MPI-3.1 standard for
more information.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<ul class="simple">
<li><p><a class="reference internal" href="MPI_Allreduce.3.html#mpi-allreduce"><span class="std std-ref">MPI_Allreduce</span></a></p></li>
<li><p><a class="reference internal" href="MPI_Reduce_scatter.3.html#mpi-reduce-scatter"><span class="std std-ref">MPI_Reduce_scatter</span></a></p></li>
<li><p><a class="reference internal" href="MPI_Scan.3.html#mpi-scan"><span class="std std-ref">MPI_Scan</span></a></p></li>
<li><p><a class="reference internal" href="MPI_Op_create.3.html#mpi-op-create"><span class="std std-ref">MPI_Op_create</span></a></p></li>
<li><p><a class="reference internal" href="MPI_Op_free.3.html#mpi-op-free"><span class="std std-ref">MPI_Op_free</span></a></p></li>
</ul>
</div>
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