Hello world exercise

hello-world/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/>.
+

hello-world/README.md

+## Parallel Hello World
+
+a) Write a simple parallel program that prints out something
+(e.g. “Hello world!”) from multiple processes. Include the MPI headers
+(C), use the MPI module (Fortran), or import mpi4py (Python) and 
+call appropriate initialization and finalization routines.
+
+b) Modify the program so that each process prints out also its rank
+and so that the process with rank 0 prints out the total number of MPI
+processes as well. 

hello-world/solution/hello.F90

+program hello
+  use mpi
+  implicit none
+  integer :: rc, myid, ntasks
+
+
+  call MPI_INIT(rc)
+
+  call MPI_COMM_SIZE(MPI_COMM_WORLD, ntasks, rc)
+  call MPI_COMM_RANK(MPI_COMM_WORLD, myid, rc)
+
+  if(myid == 0) then
+     write(*,*) 'In total there are ',ntasks, 'tasks'
+  endif
+
+  write(*,*) 'Hello from ',myid
+
+  call MPI_FINALIZE(rc)
+
+end program hello

hello-world/solution/hello.c

+#include<stdio.h>
+#include<stdlib.h>
+#include<mpi.h>
+
+int main(int argc, char *argv[])
+{
+    int i, myid, ntasks;
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
+    MPI_Comm_rank(MPI_COMM_WORLD, &myid);
+
+    if (myid == 0) {
+        printf("In total there are %i tasks\n", ntasks);
+    }
+
+    printf("Hello from %i\n", myid);
+
+    MPI_Finalize();
+    return 0;
+}

hello-world/solution/hello.py

+from __future__ import print_function
+from mpi4py import MPI
+
+comm = MPI.COMM_WORLD
+size = comm.Get_size()
+rank = comm.Get_rank()
+
+if rank == 0:
+    print("In total there are {0} tasks".format(size))
+
+print("Hello from", rank)
+