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 | */ |
---|
18 | |
---|
19 | /** |
---|
20 | \page maps2 Maps II. |
---|
21 | |
---|
22 | Here we discuss some advanced map techniques. Like writing your own maps or how to |
---|
23 | extend/modify a maps functionality with adaptors. |
---|
24 | |
---|
25 | \section custom_maps Writing Custom ReadMap |
---|
26 | \subsection custom_read_maps Readable Maps |
---|
27 | |
---|
28 | Readable maps are very frequently used as the input of an |
---|
29 | algorithm. For this purpose the most straightforward way is the use of the |
---|
30 | default maps provided by LEMON's graph structures. |
---|
31 | Very often however, it is more |
---|
32 | convenient and/or more efficient to write your own readable map. |
---|
33 | |
---|
34 | You can find some examples below. In these examples \c Graph is the |
---|
35 | type of the particular graph structure you use. |
---|
36 | |
---|
37 | |
---|
38 | This simple map assigns \f$\pi\f$ to each edge. |
---|
39 | |
---|
40 | \code |
---|
41 | struct MyMap |
---|
42 | { |
---|
43 | typedef double Value; |
---|
44 | typedef Graph::Edge Key; |
---|
45 | double operator[](const Key &e) const { return M_PI;} |
---|
46 | }; |
---|
47 | \endcode |
---|
48 | |
---|
49 | An alternative way to define maps is to use MapBase |
---|
50 | |
---|
51 | \code |
---|
52 | struct MyMap : public MapBase<Graph::Edge,double> |
---|
53 | { |
---|
54 | Value operator[](const Key& e) const { return M_PI;} |
---|
55 | }; |
---|
56 | \endcode |
---|
57 | |
---|
58 | Here is a bit more complex example. |
---|
59 | It provides a length function obtained |
---|
60 | from a base length function shifted by a potential difference. |
---|
61 | |
---|
62 | \code |
---|
63 | class ReducedLengthMap : public MapBase<Graph::Edge,double> |
---|
64 | { |
---|
65 | const Graph &g; |
---|
66 | const Graph::EdgeMap<double> &orig_len; |
---|
67 | const Graph::NodeMap<double> &pot; |
---|
68 | |
---|
69 | public: |
---|
70 | Value operator[](Key e) const { |
---|
71 | return orig_len[e]-(pot[g.target(e)]-pot[g.source(e)]); |
---|
72 | } |
---|
73 | |
---|
74 | ReducedLengthMap(const Graph &_g, |
---|
75 | const Graph::EdgeMap &_o, |
---|
76 | const Graph::NodeMap &_p) |
---|
77 | : g(_g), orig_len(_o), pot(_p) {}; |
---|
78 | }; |
---|
79 | \endcode |
---|
80 | |
---|
81 | Then, you can call e.g. Dijkstra algoritm on this map like this: |
---|
82 | \code |
---|
83 | ... |
---|
84 | ReducedLengthMap rm(g,len,pot); |
---|
85 | Dijkstra<Graph,ReducedLengthMap> dij(g,rm); |
---|
86 | dij.run(s); |
---|
87 | ... |
---|
88 | \endcode |
---|
89 | |
---|
90 | */ |
---|