Add missing dot_product.py exercise file.

python/dot_product.py

@@ -0,0 +1,35 @@
+import sys
+import numpy as np
+from mpi4py import MPI
+
+n = 8400
+
+comm = MPI.COMM_WORLD
+rank = comm.Get_rank()
+size = comm.Get_size()
+
+if n % size > 0:
+    if rank == 0:
+        sys.stderr.write("N must be a multiple of size\n")
+    comm.Abort(999)
+
+if rank == 0:
+    a = np.arange(1, n+1)
+    b = n + 1 - a
+else:
+    a = None
+    b = None
+
+nloc = n // size
+aloc = np.empty(nloc, int)
+bloc = np.empty(nloc, int)
+
+comm.Scatter(..., ..., root=0)
+comm.Scatter(..., ..., root=0)
+
+prodloc = np.dot(aloc, bloc)
+prod = comm.reduce(..., op=MPI.SUM, root=...)
+
+if rank == 0:
+    print("Inner product   = %d"%prod)
+    print("Reference value = %d"%(n * (n + 1) * (n + 2) // 6))