COIN-OR::LEMON - Graph Library

source: lemon-0.x/doc/maps1.dox @ 2553:bfced05fa852

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1/* -*- C++ -*-
2 *
3 * This file is a part of LEMON, a generic C++ optimization library
4 *
5 * Copyright (C) 2003-2008
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 */
19namespace lemon {
22\page maps1 Maps I.
24In the previous section we discussed graph topology. That is the skeleton a complex
25graph represented data-set needs. But how to assign the data itself to that skeleton?<br>
26Here come the \b maps in.
28\section maps_intro Introduction to maps
29Maps play a central role in LEMON. As their name suggests, they map a certain range of <i>keys</i> to certain <i>values</i>.
30In LEMON there is many types of maps. Each map has two typedef's to determine the types of keys and values, like this:
32  typedef Edge Key;
33  typedef double Value;
35(Except matrix maps, they have two key types.)
37To make easy to use them - especially as template parameters - there are <i>map concepts</i> like by graph classes.
39<li>\ref concepts::ReadMap "ReadMap" - values can be read out with the \c operator[].
40\code value_typed_variable = map_instance[key_value]; \endcode
42<li>\ref concepts::WriteMap "WriteMap" - values can be set with the \c set() member function.
43\code map_instance.set(key_value, value_typed_expression); \endcode
45<li>\ref concepts::ReadWriteMap "ReadWriteMap" - it's just a shortcut to indicate that the map is both
46readable and writable. It is delivered from them.
48<li>\ref concepts::ReferenceMap "ReferenceMap" - a subclass of ReadWriteMap. It has two additional typedefs
49<i>Reference</i> and <i>ConstReference</i> and two overloads of \c operator[] to
50providing you constant or non-constant reference to the value belonging to a key,
51so you have a direct access to the memory address where it is stored.
53<li>And there are the Matrix version of these maps, where the values are assigned to a pair of keys.
54The keys can be different types. (\ref concepts::ReadMatrixMap "ReadMatrixMap",
55\ref concepts::WriteMatrixMap "WriteMatrixMap", \ref concepts::ReadWriteMatrixMap "ReadWriteMatrixMap",
56\ref concepts::ReferenceMatrixMap "ReferenceMatrixMap")
60\section maps_graph Graphs' maps
61Every \ref MappableGraphComponent "mappable" graph class has two public templates: NodeMap<VALUE> and EdgeMap<VALUE>
62satisfying the \ref GraphMap concept.
63If you want to assign data to nodes, just declare a NodeMap with the corresponding
64type. As an example, think of a edge-weighted directed graph.
65\code ListGraph::EdgeMap<int>  weight(graph); \endcode
66You can see that the map needs the graph whose edges will mapped, but nothing more.
68If the graph class is extendable or erasable the map will automatically follow
69the changes you make. If a new node is added a default value is mapped to it.
70You can define the default value by passing a second argument to the map's constructor.
71\code ListGraph::EdgeMap<int>  weight(graph, 13); \endcode
72But keep in mind that \c VALUE has to have copy constructor.
74Of course \c VALUE can be a rather complex type.
76For practice let's see the following template function (from \ref maps_summary "" in the \ref demo directory)!
78\skip template
79\until }
80The task is simple. We need the summary of some kind of data assigned to a graph's nodes.
81(Whit a little trick the summary can be calculated only to a sub-graph without changing
82this code. See \ref SubGraph techniques - that's LEMON's true potential.)
84And the usage is simpler than the declaration suggests. The compiler deduces the
85template specialization, so the usage is like a simple function call.
86\skip std
87\until ;
89Most of the time you will probably use graph maps, but keep in mind, that in LEMON maps are more general and can be used widely.
91If you want some 'real-life' examples see the next page, where we discuss \ref algorithms
92(coming soon) and will use maps hardly.
93Or if you want to know more about maps read these \ref maps2 "advanced map techniques".
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