message-chain/LICENSE.txt

+
+Copyright (C) 2018  CSC - IT Center for Science Ltd.
+
+Licensed under the terms of the GNU General Public License as
+published by the Free Software Foundation, either version 3 of the
+License, or (at your option) any later version.
+
+Code is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+Copy of the GNU General Public License can be obtained from
+<http://www.gnu.org/licenses/>.
+

message-chain/README.md

+## Message chain
+
+Write a simple program where every processor sends data to the next
+one. Let ntasks be the number of the tasks, and myid the rank of the
+current process. Your program should work as follows:
+
+ - Every task with a rank less than ntasks-1 sends a message to task
+myid+1.  For example, task 0 sends a message to task 1.
+
+ - The message content is an integer array where each element is
+   initialized to myid.
+
+ - The message tag is the receiver’s id number.
+
+ - The sender prints out the number of elements it sends and the tag
+number.  All tasks with rank ≥ 1 receive messages.
+
+- Each receiver prints out their myid, and the first element in the
+  received array.
+
+ a) Implement the program described above using `MPI_Send` and
+ `MPI_Recv`. You may start from scratch or use as a starting point 
+ [c/skeleton.c](c/skeleton.c), [fortran/skeleton.F90](fortran/skeleton.F90) or
+ [python/skeleton.py](c/skeleton.py). Investigate the timings with different
+ numbers of MPI tasks (e.g. 2, 4, 8, 16, ...), and pay attention especially to
+ rank 0. Can you explain the behaviour?
+
+ b) Rewrite the program using `MPI_Sendrecv` instead of `MPI_Send` and
+`MPI_Recv`. Investigate again timings with different numbers of MPI 
+tasks (e.g. 2, 4, 8, 16, ...). Can you explain the differences to case a)?
+
+ c) Try to simplify the code by employing the `MPI_PROC_NULL` in treating the
+ special cases of the first and last task in the chain.
+
+ d) Rewrite the program using non-blocking communication (`MPI_Isend` and
+ `MPI_Irecv`).
+
+ c) Rewrite the program using persistent communication operations
+ (`MPI_Send_init`, `MPI_Recv_init`, etc.).
+