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<div class="section" id="tutorial">
<span id="id1"></span><h1>Tutorial<a class="headerlink" href="#tutorial" title="Permalink to this headline">¶</a></h1>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">Under construction. Contributions very welcome!</p>
</div>
<p><em>MPI for Python</em> supports convenient, <em>pickle</em>-based communication of
generic Python object as well as fast, near C-speed, direct array data
communication of buffer-provider objects (e.g., NumPy arrays).</p>
<ul>
<li><p class="first">Communication of generic Python objects</p>
<p>You have to use <strong>all-lowercase</strong> methods (of the <tt class="xref py py-class docutils literal"><span class="pre">Comm</span></tt>
class), like <tt class="xref py py-meth docutils literal"><span class="pre">send()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">recv()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">bcast()</span></tt>. Note
that <tt class="xref py py-meth docutils literal"><span class="pre">isend()</span></tt> is available, but <tt class="xref py py-meth docutils literal"><span class="pre">irecv()</span></tt> is not.</p>
<p>Collective calls like <tt class="xref py py-meth docutils literal"><span class="pre">scatter()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">gather()</span></tt>,
<tt class="xref py py-meth docutils literal"><span class="pre">allgather()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">alltoall()</span></tt> expect/return a sequence of
<tt class="xref py py-attr docutils literal"><span class="pre">Comm.size</span></tt> elements at the root or all process. They return a
single value, a list of <tt class="xref py py-attr docutils literal"><span class="pre">Comm.size</span></tt> elements, or
<tt class="xref py py-const docutils literal"><span class="pre">None</span></tt>.</p>
<p>Global reduction operations <tt class="xref py py-meth docutils literal"><span class="pre">reduce()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">allreduce()</span></tt>
are naively implemented, the reduction is actually done at the
designated root process or all processes.</p>
</li>
<li><p class="first">Communication of buffer-provider objects</p>
<p>You have to use method names starting with an <strong>upper-case</strong> letter
(of the <tt class="xref py py-class docutils literal"><span class="pre">Comm</span></tt> class), like <tt class="xref py py-meth docutils literal"><span class="pre">Send()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">Recv()</span></tt>,
<tt class="xref py py-meth docutils literal"><span class="pre">Bcast()</span></tt>.</p>
<p>In general, buffer arguments to these calls must be explicitly
specified by using a 2/3-list/tuple like <tt class="docutils literal"><span class="pre">[data,</span> <span class="pre">MPI.DOUBLE]</span></tt>, or
<tt class="docutils literal"><span class="pre">[data,</span> <span class="pre">count,</span> <span class="pre">MPI.DOUBLE]</span></tt> (the former one uses the byte-size of
<tt class="docutils literal"><span class="pre">data</span></tt> and the extent of the MPI datatype to define the
<tt class="docutils literal"><span class="pre">count</span></tt>).</p>
<p>Automatic MPI datatype discovery for NumPy arrays and PEP-3118
buffers is supported, but limited to basic C types (all C/C99-native
signed/unsigned integral types and single/double precision
real/complex floating types) and availability of matching datatypes
in the underlying MPI implementation. In this case, the
buffer-provider object can be passed directly as a buffer argument,
the count and MPI datatype will be inferred.</p>
</li>
</ul>
<div class="section" id="point-to-point-communication">
<h2>Point-to-Point Communication<a class="headerlink" href="#point-to-point-communication" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">Python objects (<tt class="xref py py-mod docutils literal"><span class="pre">pickle</span></tt> under the hood):</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="n">comm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">COMM_WORLD</span>
<span class="n">rank</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_rank</span><span class="p">()</span>
<span class="k">if</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="p">{</span><span class="s">'a'</span><span class="p">:</span> <span class="mi">7</span><span class="p">,</span> <span class="s">'b'</span><span class="p">:</span> <span class="mf">3.14</span><span class="p">}</span>
<span class="n">comm</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="mi">11</span><span class="p">)</span>
<span class="k">elif</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">1</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="n">source</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="mi">11</span><span class="p">)</span>
</pre></div>
</div>
</li>
<li><p class="first">NumPy arrays (the fast way!):</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="kn">import</span> <span class="nn">numpy</span>
<span class="n">comm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">COMM_WORLD</span>
<span class="n">rank</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_rank</span><span class="p">()</span>
<span class="c"># pass explicit MPI datatypes</span>
<span class="k">if</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">arange</span><span class="p">(</span><span class="mi">1000</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s">'i'</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Send</span><span class="p">([</span><span class="n">data</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">INT</span><span class="p">],</span> <span class="n">dest</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="mi">77</span><span class="p">)</span>
<span class="k">elif</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">1</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">empty</span><span class="p">(</span><span class="mi">1000</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s">'i'</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Recv</span><span class="p">([</span><span class="n">data</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">INT</span><span class="p">],</span> <span class="n">source</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="mi">77</span><span class="p">)</span>
<span class="c"># automatic MPI datatype discovery</span>
<span class="k">if</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">arange</span><span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="n">numpy</span><span class="o">.</span><span class="n">float64</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Send</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="mi">13</span><span class="p">)</span>
<span class="k">elif</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">1</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">empty</span><span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="n">numpy</span><span class="o">.</span><span class="n">float64</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Recv</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">source</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="mi">13</span><span class="p">)</span>
</pre></div>
</div>
</li>
</ul>
</div>
<div class="section" id="collective-communication">
<h2>Collective Communication<a class="headerlink" href="#collective-communication" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">Broadcasting a Python dictionary:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="n">comm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">COMM_WORLD</span>
<span class="n">rank</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_rank</span><span class="p">()</span>
<span class="k">if</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="p">{</span><span class="s">'key1'</span> <span class="p">:</span> <span class="p">[</span><span class="mi">7</span><span class="p">,</span> <span class="mf">2.72</span><span class="p">,</span> <span class="mi">2</span><span class="o">+</span><span class="mi">3</span><span class="n">j</span><span class="p">],</span>
<span class="s">'key2'</span> <span class="p">:</span> <span class="p">(</span> <span class="s">'abc'</span><span class="p">,</span> <span class="s">'xyz'</span><span class="p">)}</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="bp">None</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">bcast</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">root</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
</pre></div>
</div>
</li>
<li><p class="first">Scattering Python objects:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="n">comm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">COMM_WORLD</span>
<span class="n">size</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_size</span><span class="p">()</span>
<span class="n">rank</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_rank</span><span class="p">()</span>
<span class="k">if</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</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="o">**</span><span class="mi">2</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">size</span><span class="p">)]</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="bp">None</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">scatter</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">root</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">data</span> <span class="o">==</span> <span class="p">(</span><span class="n">rank</span><span class="o">+</span><span class="mi">1</span><span class="p">)</span><span class="o">**</span><span class="mi">2</span>
</pre></div>
</div>
</li>
<li><p class="first">Gathering Python objects:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="n">comm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">COMM_WORLD</span>
<span class="n">size</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_size</span><span class="p">()</span>
<span class="n">rank</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_rank</span><span class="p">()</span>
<span class="n">data</span> <span class="o">=</span> <span class="p">(</span><span class="n">rank</span><span class="o">+</span><span class="mi">1</span><span class="p">)</span><span class="o">**</span><span class="mi">2</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">gather</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">root</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="k">if</span> <span class="n">rank</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">size</span><span class="p">):</span>
<span class="k">assert</span> <span class="n">data</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">==</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="o">**</span><span class="mi">2</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">assert</span> <span class="n">data</span> <span class="ow">is</span> <span class="bp">None</span>
</pre></div>
</div>
</li>
<li><p class="first">Parallel matrix-vector product:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="kn">import</span> <span class="nn">numpy</span>
<span class="k">def</span> <span class="nf">matvec</span><span class="p">(</span><span class="n">comm</span><span class="p">,</span> <span class="n">A</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="n">m</span> <span class="o">=</span> <span class="n">A</span><span class="o">.</span><span class="n">shape</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="c"># local rows</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_size</span><span class="p">()</span>
<span class="n">xg</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="n">m</span><span class="o">*</span><span class="n">p</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s">'d'</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Allgather</span><span class="p">([</span><span class="n">x</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">DOUBLE</span><span class="p">],</span>
<span class="p">[</span><span class="n">xg</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">DOUBLE</span><span class="p">])</span>
<span class="n">y</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">dot</span><span class="p">(</span><span class="n">A</span><span class="p">,</span> <span class="n">xg</span><span class="p">)</span>
<span class="k">return</span> <span class="n">y</span>
</pre></div>
</div>
</li>
</ul>
</div>
<div class="section" id="dynamic-process-management">
<h2>Dynamic Process Management<a class="headerlink" href="#dynamic-process-management" title="Permalink to this headline">¶</a></h2>
<div class="section" id="compute-pi">
<h3>Compute Pi<a class="headerlink" href="#compute-pi" title="Permalink to this headline">¶</a></h3>
<ul>
<li><p class="first">Master (or parent, or client) side:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c">#!/usr/bin/env python</span>
<span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="kn">import</span> <span class="nn">numpy</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="n">comm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">COMM_SELF</span><span class="o">.</span><span class="n">Spawn</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">executable</span><span class="p">,</span>
<span class="n">args</span><span class="o">=</span><span class="p">[</span><span class="s">'cpi.py'</span><span class="p">],</span>
<span class="n">maxprocs</span><span class="o">=</span><span class="mi">5</span><span class="p">)</span>
<span class="n">N</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="s">'i'</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Bcast</span><span class="p">([</span><span class="n">N</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">INT</span><span class="p">],</span> <span class="n">root</span><span class="o">=</span><span class="n">MPI</span><span class="o">.</span><span class="n">ROOT</span><span class="p">)</span>
<span class="n">PI</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="mf">0.0</span><span class="p">,</span> <span class="s">'d'</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Reduce</span><span class="p">(</span><span class="bp">None</span><span class="p">,</span> <span class="p">[</span><span class="n">PI</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">DOUBLE</span><span class="p">],</span>
<span class="n">op</span><span class="o">=</span><span class="n">MPI</span><span class="o">.</span><span class="n">SUM</span><span class="p">,</span> <span class="n">root</span><span class="o">=</span><span class="n">MPI</span><span class="o">.</span><span class="n">ROOT</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="n">PI</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Disconnect</span><span class="p">()</span>
</pre></div>
</div>
</li>
<li><p class="first">Worker (or child, or server) side:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c">#!/usr/bin/env python</span>
<span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="kn">import</span> <span class="nn">numpy</span>
<span class="n">comm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">Comm</span><span class="o">.</span><span class="n">Get_parent</span><span class="p">()</span>
<span class="n">size</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_size</span><span class="p">()</span>
<span class="n">rank</span> <span class="o">=</span> <span class="n">comm</span><span class="o">.</span><span class="n">Get_rank</span><span class="p">()</span>
<span class="n">N</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s">'i'</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Bcast</span><span class="p">([</span><span class="n">N</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">INT</span><span class="p">],</span> <span class="n">root</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="n">h</span> <span class="o">=</span> <span class="mf">1.0</span> <span class="o">/</span> <span class="n">N</span><span class="p">;</span> <span class="n">s</span> <span class="o">=</span> <span class="mf">0.0</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">rank</span><span class="p">,</span> <span class="n">N</span><span class="p">,</span> <span class="n">size</span><span class="p">):</span>
<span class="n">x</span> <span class="o">=</span> <span class="n">h</span> <span class="o">*</span> <span class="p">(</span><span class="n">i</span> <span class="o">+</span> <span class="mf">0.5</span><span class="p">)</span>
<span class="n">s</span> <span class="o">+=</span> <span class="mf">4.0</span> <span class="o">/</span> <span class="p">(</span><span class="mf">1.0</span> <span class="o">+</span> <span class="n">x</span><span class="o">**</span><span class="mi">2</span><span class="p">)</span>
<span class="n">PI</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="n">s</span> <span class="o">*</span> <span class="n">h</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s">'d'</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Reduce</span><span class="p">([</span><span class="n">PI</span><span class="p">,</span> <span class="n">MPI</span><span class="o">.</span><span class="n">DOUBLE</span><span class="p">],</span> <span class="bp">None</span><span class="p">,</span>
<span class="n">op</span><span class="o">=</span><span class="n">MPI</span><span class="o">.</span><span class="n">SUM</span><span class="p">,</span> <span class="n">root</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="n">comm</span><span class="o">.</span><span class="n">Disconnect</span><span class="p">()</span>
</pre></div>
</div>
</li>
</ul>
</div>
</div>
<div class="section" id="wrapping-with-swig">
<h2>Wrapping with SWIG<a class="headerlink" href="#wrapping-with-swig" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">C source:</p>
<div class="highlight-c"><div class="highlight"><pre><span class="cm">/* file: helloworld.c */</span>
<span class="kt">void</span> <span class="nf">sayhello</span><span class="p">(</span><span class="n">MPI_Comm</span> <span class="n">comm</span><span class="p">)</span>
<span class="p">{</span>
<span class="kt">int</span> <span class="n">size</span><span class="p">,</span> <span class="n">rank</span><span class="p">;</span>
<span class="n">MPI_Comm_size</span><span class="p">(</span><span class="n">comm</span><span class="p">,</span> <span class="o">&</span><span class="n">size</span><span class="p">);</span>
<span class="n">MPI_Comm_rank</span><span class="p">(</span><span class="n">comm</span><span class="p">,</span> <span class="o">&</span><span class="n">rank</span><span class="p">);</span>
<span class="n">printf</span><span class="p">(</span><span class="s">"Hello, World! "</span>
<span class="s">"I am process %d of %d.</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span>
<span class="n">rank</span><span class="p">,</span> <span class="n">size</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
<li><p class="first">SWIG interface file:</p>
<div class="highlight-c"><div class="highlight"><pre><span class="c1">// file: helloworld.i</span>
<span class="o">%</span><span class="n">module</span> <span class="n">helloworld</span>
<span class="o">%</span><span class="p">{</span>
<span class="cp">#include <mpi.h></span>
<span class="cp">#include "helloworld.c"</span>
<span class="p">}</span><span class="o">%</span>
<span class="o">%</span><span class="n">include</span> <span class="n">mpi4py</span><span class="o">/</span><span class="n">mpi4py</span><span class="p">.</span><span class="n">i</span>
<span class="o">%</span><span class="n">mpi4py_typemap</span><span class="p">(</span><span class="n">Comm</span><span class="p">,</span> <span class="n">MPI_Comm</span><span class="p">);</span>
<span class="kt">void</span> <span class="n">sayhello</span><span class="p">(</span><span class="n">MPI_Comm</span> <span class="n">comm</span><span class="p">);</span>
</pre></div>
</div>
</li>
<li><p class="first">Try it in the Python prompt:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="gp">>>> </span><span class="kn">import</span> <span class="nn">helloworld</span>
<span class="gp">>>> </span><span class="n">helloworld</span><span class="o">.</span><span class="n">sayhello</span><span class="p">(</span><span class="n">MPI</span><span class="o">.</span><span class="n">COMM_WORLD</span><span class="p">)</span>
<span class="go">Hello, World! I am process 0 of 1.</span>
</pre></div>
</div>
</li>
</ul>
</div>
<div class="section" id="wrapping-with-f2py">
<h2>Wrapping with F2Py<a class="headerlink" href="#wrapping-with-f2py" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">Fortran 90 source:</p>
<div class="highlight-fortran"><div class="highlight"><pre><span class="c">! file: helloworld.f90</span>
<span class="k">subroutine </span><span class="nv">sayhello</span><span class="p">(</span><span class="nv">comm</span><span class="p">)</span>
<span class="k">use </span><span class="nv">mpi</span>
<span class="k">implicit none</span>
<span class="k"> </span><span class="kt">integer</span> <span class="kd">::</span> <span class="nv">comm</span><span class="p">,</span> <span class="nv">rank</span><span class="p">,</span> <span class="nv">size</span><span class="p">,</span> <span class="nv">ierr</span>
<span class="k">call </span><span class="nv">MPI_Comm_size</span><span class="p">(</span><span class="nv">comm</span><span class="p">,</span> <span class="nv">size</span><span class="p">,</span> <span class="nv">ierr</span><span class="p">)</span>
<span class="k">call </span><span class="nv">MPI_Comm_rank</span><span class="p">(</span><span class="nv">comm</span><span class="p">,</span> <span class="nv">rank</span><span class="p">,</span> <span class="nv">ierr</span><span class="p">)</span>
<span class="k">print</span> <span class="o">*</span><span class="p">,</span> <span class="s1">'Hello, World! I am process '</span><span class="p">,</span><span class="nv">rank</span><span class="p">,</span><span class="s1">' of '</span><span class="p">,</span><span class="nv">size</span><span class="p">,</span><span class="s1">'.'</span>
<span class="k">end subroutine </span><span class="nv">sayhello</span>
</pre></div>
</div>
</li>
<li><p class="first">Try it in the Python prompt:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">mpi4py</span> <span class="kn">import</span> <span class="n">MPI</span>
<span class="gp">>>> </span><span class="kn">import</span> <span class="nn">helloworld</span>
<span class="gp">>>> </span><span class="n">fcomm</span> <span class="o">=</span> <span class="n">MPI</span><span class="o">.</span><span class="n">COMM_WORLD</span><span class="o">.</span><span class="n">py2f</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">helloworld</span><span class="o">.</span><span class="n">sayhello</span><span class="p">(</span><span class="n">fcomm</span><span class="p">)</span>
<span class="go">Hello, World! I am process 0 of 1.</span>
</pre></div>
</div>
</li>
</ul>
</div>
</div>
</div>
</div>
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<li><a class="reference internal" href="#">Tutorial</a><ul>
<li><a class="reference internal" href="#point-to-point-communication">Point-to-Point Communication</a></li>
<li><a class="reference internal" href="#collective-communication">Collective Communication</a></li>
<li><a class="reference internal" href="#dynamic-process-management">Dynamic Process Management</a><ul>
<li><a class="reference internal" href="#compute-pi">Compute Pi</a></li>
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<li><a class="reference internal" href="#wrapping-with-swig">Wrapping with SWIG</a></li>
<li><a class="reference internal" href="#wrapping-with-f2py">Wrapping with F2Py</a></li>
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