1 | namespace lemon { |
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2 | /** |
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3 | |
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4 | \ingroup demos |
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5 | \file graph_orientation.cc |
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6 | \brief Graph orientation with lower bound requirement on the |
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7 | in-degree of the nodes. |
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8 | |
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9 | |
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10 | |
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11 | First we include some important headers. |
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12 | |
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13 | The first one defines \ref lemon::ListGraph "ListGraph", |
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14 | the "Swiss army knife" graph implementation. |
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15 | \dontinclude graph_orientation.cc |
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16 | \skipline list_graph |
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17 | |
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18 | The next is to read a \ref graph-io-page ".lgf" (Lemon Graph Format) file. |
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19 | \skipline reader |
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20 | |
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21 | This provides us with some special purpose graph \ref maps "maps". |
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22 | \skipline iterable |
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23 | |
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24 | The following header defines a simple data structure to store and manipulate |
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25 | planar coordinates. It will be used to draw the result. |
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26 | \skipline xy |
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27 | |
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28 | And finally, this header contains a simple graph drawing utility. |
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29 | \skipline eps |
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30 | |
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31 | As we don't want to type in \ref lemon "lemon::" million times, the |
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32 | following line seems to be useful. |
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33 | \skipline namespace |
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34 | |
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35 | The following <tt>typedef</tt>s will also save a lot of typing. |
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36 | \skip typedef |
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37 | \until InEdgeIt |
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38 | |
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39 | Well, we are ready to start <tt>main()</tt>. |
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40 | \skip main |
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41 | \until { |
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42 | |
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43 | First we check whether the program is called with exactly 1 parameter. |
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44 | If it isn't, we print a short help message end exit. |
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45 | The vast majority of people would probably skip this block. |
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46 | \skip if |
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47 | \until } |
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48 | |
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49 | Now, we read a graph \c g, and a map \c f containing |
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50 | the in-deg requirements from a \ref graph-io-page ".lgf" (Lemon Graph Format) |
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51 | file. To generate the output picture, we also read the node titles (\c id) and |
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52 | coordinates (\c coords). |
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53 | So, first we create the graph |
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54 | \skipline ListGraph |
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55 | and the corresponding NodeMaps. |
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56 | \skipline NodeMap |
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57 | \until coords |
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58 | \note The graph must be given to the maps' constructor. |
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59 | |
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60 | Then, the following block will read these data from the file, or exit if |
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61 | the file is missing or corrupt. |
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62 | \skip try |
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63 | \until } |
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64 | \until } |
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65 | |
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66 | The algorithm needs a "level" integer value assigned to each node. In the |
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67 | beginning, the nodes are on level 0. |
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68 | \skipline level |
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69 | |
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70 | The deficiency (\c def) of a node is the in-degree requirement minus the |
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71 | actual in-degree. |
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72 | |
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73 | \skip def |
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74 | \until subMap |
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75 | |
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76 | A node is \e active if its deficiency is positive (i.e. if it doesn't meet |
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77 | the degree requirement). |
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78 | \skip active |
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79 | \until def |
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80 | |
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81 | We also store in a bool map which edges are reverted. Actually this is only |
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82 | used to draw these edges with different color in the output picture. The |
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83 | algorithm will update this map called \c rev, but will not use it otherwise. |
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84 | \skip rev |
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85 | \until reversed |
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86 | |
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87 | The variable \c nodeNum will refer to the number of nodes. |
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88 | \skipline nodeNum |
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89 | |
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90 | Here comes the algorithms itself. |
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91 | In each iteration we choose an active node (\c act will store it). If there is |
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92 | no such a node, then the orientation is feasible so we are done. |
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93 | \skip act |
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94 | \until while |
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95 | |
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96 | Then we check if there exists an edge leaving this node that steps down exactly |
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97 | one level. |
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98 | \skip OutEdge |
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99 | \until while |
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100 | |
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101 | If there exists, we decrease the "activity" of the node \c act by reverting |
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102 | this egde. |
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103 | Fortunately, \ref lemon::ListGraph "ListGraph" |
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104 | has a special function \ref lemon::ListGraph::reverseEdge() "reverseEdge()" |
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105 | that makes this easy. |
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106 | We also have to update the maps \c def and |
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107 | \c rev. |
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108 | \skipline if |
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109 | \skip if |
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110 | \until } |
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111 | Otherwise (i.e. if there is no edge stepping down one level). We lift up the |
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112 | current active node \c act. If it reaches level \c nodeNum, then there |
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113 | exists no appropriate orientation so we stop. |
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114 | \skipline else |
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115 | \skipline if |
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116 | \skipline return |
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117 | \until } |
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118 | \until } |
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119 | \until } |
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120 | |
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121 | Believe it or not, this algorithm works and runs fast. |
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122 | |
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123 | Finally, we print the obtained orientation. Note, how the different |
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124 | \c bool values of |
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125 | \c rev are transformed into different \ref lemon::Color "RGB color"s |
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126 | using the class |
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127 | \ref lemon::ColorSet "ColorSet" |
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128 | and the \ref map_adaptors "map adaptor" called |
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129 | \ref lemon::ComposeMap "composeMap". |
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130 | |
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131 | \skip graphToEps |
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132 | \until run |
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133 | |
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134 | |
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135 | \until end of main |
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136 | |
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137 | Finally here are again the list of the used include files (because I can't turn |
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138 | this section off.) |
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139 | |
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140 | */ |
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141 | |
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142 | } |
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