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7<title>Parallel BGL METIS Input Routines</title>
8<link rel="stylesheet" href="../../../../rst.css" type="text/css" />
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10<body>
11<div class="document" id="logo-metis-input-routines">
12<h1 class="title"><a class="reference external" href="http://www.osl.iu.edu/research/pbgl"><img align="middle" alt="Parallel BGL" class="align-middle" src="pbgl-logo.png" /></a> METIS Input Routines</h1>
13
14<!-- Copyright (C) 2004-2008 The Trustees of Indiana University.
15Use, modification and distribution is subject to the Boost Software
16License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
17http://www.boost.org/LICENSE_1_0.txt) -->
18<pre class="literal-block">
19namespace boost {
20 namespace graph {
21 class metis_reader;
22 class metis_exception;
23 class metis_input_exception;
24 class metis_distribution;
25 }
26}
27</pre>
28<p><a class="reference external" href="http://www-users.cs.umn.edu/~karypis/metis/metis/">METIS</a> is a set of programs for partitioning graphs (among other
29things). The Parallel BGL can read the METIS graph format and
30partition format, allowing one to easily load METIS-partitioned
31graphs into the Parallel BGL's data structures.</p>
32<div class="contents topic" id="contents">
33<p class="topic-title first">Contents</p>
34<ul class="simple">
35<li><a class="reference internal" href="#where-defined" id="id3">Where Defined</a><ul>
36<li><a class="reference internal" href="#graph-reader" id="id4">Graph Reader</a></li>
37</ul>
38</li>
39<li><a class="reference internal" href="#usage" id="id5">Usage</a></li>
40<li><a class="reference internal" href="#associated-types" id="id6">Associated Types</a></li>
41<li><a class="reference internal" href="#member-functions" id="id7">Member Functions</a><ul>
42<li><a class="reference internal" href="#partition-reader" id="id8">Partition Reader</a></li>
43</ul>
44</li>
45<li><a class="reference internal" href="#id1" id="id9">Usage</a></li>
46<li><a class="reference internal" href="#id2" id="id10">Member Functions</a></li>
47</ul>
48</div>
49<div class="section" id="where-defined">
50<h1><a class="toc-backref" href="#id3">Where Defined</a></h1>
51<p>&lt;<tt class="docutils literal"><span class="pre">boost/graph/metis.hpp</span></tt>&gt;</p>
52<div class="section" id="graph-reader">
53<h2><a class="toc-backref" href="#id4">Graph Reader</a></h2>
54<pre class="literal-block">
55class metis_reader
56{
57 public:
58 typedef std::size_t vertices_size_type;
59 typedef std::size_t edges_size_type;
60 typedef double vertex_weight_type;
61 typedef double edge_weight_type;
62
63 class edge_iterator;
64 class edge_weight_iterator;
65
66 metis_reader(std::istream&amp; in);
67
68 edge_iterator begin();
69 edge_iterator end();
70 edge_weight_iterator weight_begin();
71
72 vertices_size_type num_vertices() const;
73 edges_size_type num_edges() const;
74
75 std::size_t num_vertex_weights() const;
76
77 vertex_weight_type vertex_weight(vertices_size_type v, std::size_t n);
78
79 bool has_edge_weights() const;
80};
81</pre>
82</div>
83</div>
84<div class="section" id="usage">
85<h1><a class="toc-backref" href="#id5">Usage</a></h1>
86<p>The METIS reader provides an iterator interface to the METIS graph
87file. The iterator interface is most useful when constructing Parallel
88BGL graphs on-the-fly. For instance, the following code builds a graph
89<tt class="docutils literal"><span class="pre">g</span></tt> from a METIS graph stored in <tt class="docutils literal"><span class="pre">argv[1]</span></tt>.</p>
90<pre class="literal-block">
91std::ifstream in_graph(argv[1]);
92metis_reader reader(in_graph);
93Graph g(reader.begin(), reader.end(),
94 reader.weight_begin(),
95 reader.num_vertices());
96</pre>
97<p>The calls to <tt class="docutils literal"><span class="pre">begin()</span></tt> and <tt class="docutils literal"><span class="pre">end()</span></tt> return an iterator range for
98the edges in the graph; the call to <tt class="docutils literal"><span class="pre">weight_begin()</span></tt> returns an
99iterator that will enumerate the weights of the edges in the
100graph. For a distributed graph, the distribution will be determined
101automatically by the graph; to use a METIS partitioning, see the
102section <a class="reference internal" href="#partition-reader">Partition Reader</a>.</p>
103</div>
104<div class="section" id="associated-types">
105<h1><a class="toc-backref" href="#id6">Associated Types</a></h1>
106<pre class="literal-block">
107metis_reader::edge_iterator
108</pre>
109<p>An <a class="reference external" href="http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a> that enumerates the edges in the METIS graph, and
110is suitable for use as the <tt class="docutils literal"><span class="pre">EdgeIterator</span></tt> of an <a class="reference external" href="http://www.boost.org/libs/graph/doc/adjacency_list.html">adjacency_list</a>.
111The <tt class="docutils literal"><span class="pre">value_type</span></tt> of this iterator is a pair of vertex numbers.</p>
112<hr class="docutils" />
113<pre class="literal-block">
114metis_reader::edge_weight_iterator
115</pre>
116<p>An <a class="reference external" href="http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a> that enumerates the edge weights in the METIS
117graph. The <tt class="docutils literal"><span class="pre">value_type</span></tt> of this iterator is <tt class="docutils literal"><span class="pre">edge_weight_type</span></tt>. If
118the edges in the METIS graph are unweighted, the result of
119dereferencing this iterator will always be zero.</p>
120</div>
121<div class="section" id="member-functions">
122<h1><a class="toc-backref" href="#id7">Member Functions</a></h1>
123<pre class="literal-block">
124metis_reader(std::istream&amp; in);
125</pre>
126<p>Constructs a new METIS reader that will retrieve edges from the input
127stream <tt class="docutils literal"><span class="pre">in</span></tt>. If any errors are encountered while initially parsing
128<tt class="docutils literal"><span class="pre">in</span></tt>, <tt class="docutils literal"><span class="pre">metis_input_exception</span></tt> will be thrown.</p>
129<hr class="docutils" />
130<pre class="literal-block">
131edge_iterator begin();
132</pre>
133<p>Returns an iterator to the first edge in the METIS file.</p>
134<hr class="docutils" />
135<pre class="literal-block">
136edge_iterator end();
137</pre>
138<p>Returns an iterator one past the last edge in the METIS file.</p>
139<hr class="docutils" />
140<pre class="literal-block">
141edge_weight_iterator weight_begin();
142</pre>
143<p>Returns an iterator to the first edge weight in the METIS file. The
144weight iterator should be moved in concert with the edge iterator;
145when the edge iterator moves, the edge weight changes. If the edges
146in the graph are unweighted, the weight returned will always be zero.</p>
147<hr class="docutils" />
148<pre class="literal-block">
149vertices_size_type num_vertices() const;
150</pre>
151<p>Returns the number of vertices in the graph.</p>
152<hr class="docutils" />
153<pre class="literal-block">
154edges_size_type num_edges() const;
155</pre>
156<p>Returns the number of edges in the graph.</p>
157<hr class="docutils" />
158<pre class="literal-block">
159std::size_t num_vertex_weights() const;
160</pre>
161<p>Returns the number of weights attached to each vertex.</p>
162<hr class="docutils" />
163<pre class="literal-block">
164vertex_weight_type vertex_weight(vertices_size_type v, std::size_t n);
165</pre>
166<hr class="docutils" />
167<pre class="literal-block">
168bool has_edge_weights() const;
169</pre>
170<p>Returns <tt class="docutils literal"><span class="pre">true</span></tt> when the edges of the graph have weights, <tt class="docutils literal"><span class="pre">false</span></tt>
171otherwise. When <tt class="docutils literal"><span class="pre">false</span></tt>, the edge weight iterator is still valid
172but returns zero for the weight of each edge.</p>
173<div class="section" id="partition-reader">
174<h2><a class="toc-backref" href="#id8">Partition Reader</a></h2>
175<pre class="literal-block">
176class metis_distribution
177{
178 public:
179 typedef int process_id_type;
180 typedef std::size_t size_type;
181
182 metis_distribution(std::istream&amp; in, process_id_type my_id);
183
184 size_type block_size(process_id_type id, size_type) const;
185 process_id_type operator()(size_type n);
186 size_type local(size_type n) const;
187 size_type global(size_type n) const;
188 size_type global(process_id_type id, size_type n) const;
189
190 private:
191 std::istream&amp; in;
192 process_id_type my_id;
193 std::vector&lt;process_id_type&gt; vertices;
194};
195</pre>
196</div>
197</div>
198<div class="section" id="id1">
199<h1><a class="toc-backref" href="#id9">Usage</a></h1>
200<p>The class <tt class="docutils literal"><span class="pre">metis_distribution</span></tt> loads a METIS partition file and
201makes it available as a Distribution suitable for use with the
202<a class="reference external" href="distributed_adjacency_list.html">distributed adjacency list</a> graph type. To load a METIS graph using
203a METIS partitioning, use a <tt class="docutils literal"><span class="pre">metis_reader</span></tt> object for the graph and
204a <tt class="docutils literal"><span class="pre">metis_distribution</span></tt> object for the distribution, as in the
205following example.</p>
206<pre class="literal-block">
207std::ifstream in_graph(argv[1]);
208metis_reader reader(in_graph);
209
210std::ifstream in_partitions(argv[2]);
211metis_distribution dist(in_partitions, process_id(pg));
212Graph g(reader.begin(), reader.end(),
213 reader.weight_begin(),
214 reader.num_vertices(),
215 pg,
216 dist);
217</pre>
218<p>In this example, <tt class="docutils literal"><span class="pre">argv[1]</span></tt> is the graph and <tt class="docutils literal"><span class="pre">argv[2]</span></tt> is the
219partition file generated by <tt class="docutils literal"><span class="pre">pmetis</span></tt>. The <tt class="docutils literal"><span class="pre">dist</span></tt> object loads the
220partitioning information from the input stream it is given and uses
221that to distributed the adjacency list. Note that the input stream
222must be in the METIS partition file format and must have been
223partitioned for the same number of processes are there are in the
224process group <tt class="docutils literal"><span class="pre">pg</span></tt>.</p>
225</div>
226<div class="section" id="id2">
227<h1><a class="toc-backref" href="#id10">Member Functions</a></h1>
228<pre class="literal-block">
229metis_distribution(std::istream&amp; in, process_id_type my_id);
230</pre>
231<p>Creates a new METIS distribution from the input stream
232<tt class="docutils literal"><span class="pre">in</span></tt>. <tt class="docutils literal"><span class="pre">my_id</span></tt> is the process ID of the current process in the
233process group over which the graph will be distributed.</p>
234<hr class="docutils" />
235<pre class="literal-block">
236size_type block_size(process_id_type id, size_type) const;
237</pre>
238<p>Returns the number of vertices to be stored in the process
239<tt class="docutils literal"><span class="pre">id</span></tt>. The second parameter, <tt class="docutils literal"><span class="pre">size_type</span></tt>, is unused and may be any
240value.</p>
241<hr class="docutils" />
242<pre class="literal-block">
243process_id_type operator()(size_type n);
244</pre>
245<p>Returns the ID for the process that will store vertex number <tt class="docutils literal"><span class="pre">n</span></tt>.</p>
246<hr class="docutils" />
247<pre class="literal-block">
248size_type local(size_type n) const;
249</pre>
250<p>Returns the local index of vertex number <tt class="docutils literal"><span class="pre">n</span></tt> within its owning
251process.</p>
252<hr class="docutils" />
253<pre class="literal-block">
254size_type global(size_type n) const;
255</pre>
256<p>Returns the global index of the current processor's local vertex <tt class="docutils literal"><span class="pre">n</span></tt>.</p>
257<hr class="docutils" />
258<pre class="literal-block">
259size_type global(process_id_type id, size_type n) const;
260</pre>
261<p>Returns the global index of the process <tt class="docutils literal"><span class="pre">id</span></tt>'s local vertex <tt class="docutils literal"><span class="pre">n</span></tt>.</p>
262<hr class="docutils" />
263<p>Copyright (C) 2005 The Trustees of Indiana University.</p>
264<p>Authors: Douglas Gregor and Andrew Lumsdaine</p>
265</div>
266</div>
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269Generated on: 2009-05-31 00:21 UTC.
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