COIN-OR::LEMON - Graph Library

source: lemon-0.x/doc/read_write_bg.dox @ 2391:14a343be7a5a

Last change on this file since 2391:14a343be7a5a was 2391:14a343be7a5a, checked in by Alpar Juttner, 13 years ago

Happy New Year to all source files!

File size: 7.6 KB
Line 
1/* -*- C++ -*-
2 *
3 * This file is a part of LEMON, a generic C++ optimization library
4 *
5 * Copyright (C) 2003-2007
6 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
7 * (Egervary Research Group on Combinatorial Optimization, EGRES).
8 *
9 * Permission to use, modify and distribute this software is granted
10 * provided that this copyright notice appears in all copies. For
11 * precise terms see the accompanying LICENSE file.
12 *
13 * This software is provided "AS IS" with no warranty of any kind,
14 * express or implied, and with no claim as to its suitability for any
15 * purpose.
16 *
17 */
18
19namespace lemon {
20/*!
21\page read_write_bg Background of Reading and Writing
22
23To read a map (on the nodes or edges)
24the \ref lemon::GraphReader "GraphReader"
25should know how to read a Value from the given map.
26By the default implementation the input operator reads a value from
27the stream and the type of the read value is the value type of the given map.
28When the reader should skip a value in the stream, because you do not
29want to store it in a map, the reader skips a character sequence without
30whitespaces.
31
32If you want to change the functionality of the reader, you can use
33template parameters to specialize it. When you give a reading
34command for a map you can give a Reader type as template parameter.
35With this template parameter you can control how the Reader reads
36a value from the stream.
37
38The reader has the next structure:
39\code
40struct TypeReader {
41  typedef TypeName Value;
42
43  void read(std::istream& is, Value& value);
44};
45\endcode
46
47For example, the \c "strings" nodemap contains strings and you do not need
48the value of the string just the length. Then you can implement an own Reader
49struct.
50
51\code
52struct LengthReader {
53  typedef int Value;
54
55  void read(std::istream& is, Value& value) {
56    std::string tmp;
57    is >> tmp;
58    value = tmp.length();
59  }
60};
61...
62reader.readNodeMap<LengthReader>("strings", lengthMap);
63\endcode 
64
65The global functionality of the reader class can be changed by giving a
66special template parameter to the GraphReader class. By default, the
67template parameter is \c DefaultReaderTraits. A reader traits class
68should provide a nested template class Reader for each type, and a
69DefaultReader for skipping a value.
70
71The specialization of writing is very similar to that of reading.
72
73\section u Undirected graphs
74
75In a file describing an undirected graph (ugraph, for short) you find an
76\c uedgeset section instead of the \c edgeset section. The first line of
77the section describes the names of the maps on the undirected egdes and all
78next lines describe one undirected edge with the the incident nodes and the
79values of the map.
80
81The format handles directed edge maps as a syntactical sugar???, if there
82are two maps with names being the same with a \c '+' and a \c '-' prefix
83then this will be read as a directed map.
84
85\code
86@uedgeset
87             label      capacity        +flow   -flow
8832   2       1          4.3             2.0     0.0
8921   21      5          2.6             0.0     2.6
9021   12      8          3.4             0.0     0.0
91\endcode
92
93The \c edges section is changed to \c uedges section. This section
94describes labeled edges and undirected edges. The directed edge label
95should start with a \c '+' or a \c '-' prefix to decide the direction
96of the edge.
97
98\code
99@uedges
100uedge 1
101+edge 5
102-back 5
103\endcode
104
105There are similar classes to the \ref lemon::GraphReader "GraphReader" and
106\ref lemon::GraphWriter "GraphWriter" which
107handle the undirected graphs. These classes are
108the \ref lemon::UGraphReader "UGraphReader"
109and \ref lemon::UGraphWriter "UGraphWriter".
110
111The \ref lemon::UGraphReader::readUEdgeMap() "readUEdgeMap()"
112function reads an undirected map and the
113\ref lemon::UGraphReader::readUEdge() "readUEdge()"
114reads an undirected edge from the file,
115
116\code
117reader.readUEdgeMap("capacity", capacityMap);
118reader.readEdgeMap("flow", flowMap);
119...
120reader.readUEdge("u_edge", u_edge);
121reader.readEdge("edge", edge);
122\endcode
123
124\section advanced Advanced features
125
126The graph reader and writer classes give an easy way to read and write
127graphs. But sometimes we want more advanced features. In this case we can
128use the more general <tt>lemon reader and writer</tt> interface.
129
130The LEMON file format is a section oriented file format. It contains one or
131more sections, each starting with a line identifying its type
132(the word starting with the \c \@  character).
133The content of the section this way cannot contain line with \c \@ first
134character. The file may contains comment lines with \c # first character.
135
136The \ref lemon::LemonReader "LemonReader"
137and \ref lemon::LemonWriter "LemonWriter"
138gives a framework to read and
139write sections. There are various section reader and section writer
140classes which can be attached to a \ref lemon::LemonReader "LemonReader"
141or a \ref lemon::LemonWriter "LemonWriter".
142
143There are default section readers and writers for reading and writing
144item sets, and labeled items in the graph. These read and write
145the format described above. Other type of data can be handled with own
146section reader and writer classes which are inherited from the
147\c LemonReader::SectionReader or the
148\ref lemon::LemonWriter::SectionWriter "LemonWriter::SectionWriter"
149classes.
150
151The next example defines a special section reader which reads the
152\c \@description sections into a string:
153
154\code
155class DescriptionReader : LemonReader::SectionReader {
156protected:
157  virtual bool header(const std::string& line) {
158    std::istringstream ls(line);
159    std::string head;
160    ls >> head;
161    return head == "@description";
162  }
163
164  virtual void read(std::istream& is) {
165    std::string line;
166    while (getline(is, line)) {
167      desc += line;
168    }
169  }
170public:
171
172  typedef LemonReader::SectionReader Parent;
173 
174  DescriptionReader(LemonReader& reader) : Parent(reader) {}
175
176  const std::string& description() const {
177    return description;
178  }
179
180private:
181  std::string desc;
182};
183\endcode
184
185The other advanced stuff of the generalized file format is that
186multiple edgesets can be stored to the same nodeset. It can be used
187for example as a network traffic matrix.
188
189In our example there is a network with symmetric links and there are assymetric
190traffic request on the network. This construction can be stored in an
191undirected graph and in a directed \c ListEdgeSet class. The example
192shows the input with the \ref lemon::LemonReader "LemonReader" class:
193
194\code
195ListUGraph network;
196ListUGraph::UEdgeMap<double> capacity;
197ListEdgeSet<ListUGraph> traffic(network);
198ListEdgeSet<ListUGraph>::EdgeMap<double> request(network);
199
200LemonReader reader(std::cin);
201NodeSetReader<ListUGraph> nodesetReader(reader, network);
202UEdgeSetReader<ListUGraph>
203  uEdgesetReader(reader, network, nodesetReader);
204uEdgesetReader.readEdgeMap("capacity", capacity);
205EdgeSetReader<ListEdgeSet<ListUGraph> >
206  edgesetReader(reader, traffic, nodesetReader, "traffic");
207edgesetReader.readEdgeMap("request", request);
208
209reader.run();
210\endcode
211
212Because both the \ref lemon::GraphReader "GraphReader"
213and the \ref lemon::UGraphReader "UGraphReader" can be converted
214to \ref lemon::LemonReader "LemonReader"
215and it can resolve the label's of the items, the previous
216result can be achived with the \ref lemon::UGraphReader "UGraphReader"
217class, too.
218
219
220\code
221ListUGraph network;
222ListUGraph::UEdgeSet<double> capacity;
223ListEdgeSet<ListUGraph> traffic(network);
224ListEdgeSet<ListUGraph>::EdgeMap<double> request(network);
225
226UGraphReader<ListUGraph> reader(std::cin, network);
227reader.readEdgeMap("capacity", capacity);
228EdgeSetReader<ListEdgeSet<ListUGraph> >
229  edgesetReader(reader, traffic, reader, "traffic");
230edgesetReader.readEdgeMap("request", request);
231
232reader.run();
233\endcode
234
235\author Balazs Dezso
236*/
237}
Note: See TracBrowser for help on using the repository browser.