From 7fdfbca0bd1ac63f0c18a2053b3b00d0d671f528 2009-10-14 23:16:59
From: Brian Granger <ellisonbg@gmail.com>
Date: 2009-10-14 23:16:59
Subject: [PATCH] Fix in MPI psum example.

Thanks to J. Thomas for updating the psum example to the mpi4py
1.1.0 API.

---

diff --git a/docs/source/parallel/parallel_mpi.txt b/docs/source/parallel/parallel_mpi.txt
index 45fc61f..cdb54df 100644
--- a/docs/source/parallel/parallel_mpi.txt
+++ b/docs/source/parallel/parallel_mpi.txt
@@ -85,7 +85,7 @@ Actually using MPI
 Once the engines are running with MPI enabled, you are ready to go. You can
 now call any code that uses MPI in the IPython engines. And, all of this can
 be done interactively. Here we show a simple example that uses mpi4py
-[mpi4py]_.
+[mpi4py]_ version 1.1.0 or later.
 
 First, lets define a simply function that uses MPI to calculate the sum of a
 distributed array. Save the following text in a file called :file:`psum.py`:
@@ -94,10 +94,14 @@ distributed array. Save the following text in a file called :file:`psum.py`:
 
     from mpi4py import MPI
     import numpy as np
-    
+
     def psum(a):
         s = np.sum(a)
-        return MPI.COMM_WORLD.Allreduce(s,MPI.SUM)
+        rcvBuf = np.array(0.0,'d')
+        MPI.COMM_WORLD.Allreduce([s, MPI.DOUBLE],
+            [rcvBuf, MPI.DOUBLE],
+            op=MPI.SUM)
+        return rcvBuf
 
 Now, start an IPython cluster in the same directory as :file:`psum.py`::