COIN-OR::LEMON - Graph Library

source: lemon-0.x/doc/quicktour.dox @ 1511:d6b95a59da26

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[1170]3\page quicktour Quick Tour to LEMON
[1175]5Let us first answer the question <b>"What do I want to use LEMON for?"
7LEMON is a C++ library, so you can use it if you want to write C++
8programs. What kind of tasks does the library LEMON help to solve?
9It helps to write programs that solve optimization problems that arise
10frequently when <b>designing and testing certain networks</b>, for example
11in telecommunication, computer networks, and other areas that I cannot
12think of now. A very natural way of modelling these networks is by means
[1183]13of a <b> graph</b> (we will always mean a directed graph by that and say
14<b> undirected graph </b> otherwise).
[1175]15So if you want to write a program that works with
[1183]16graphs then you might find it useful to use our library LEMON. LEMON
17defines various graph concepts depending on what you want to do with the
18graph: a very good description can be found in the page
19about \ref graphs "graphs".
[1511]21You will also want to assign data to the edges or nodes of the graph, for example a length or capacity function defined on the edges. You can do this in LEMON using so called \ref maps "maps". You can define a map on the nodes or on the edges of the graph and the value of the map (the range of the function) can be practically almost of any type. Read more about maps \ref maps-page "here".
[1511]23Some examples are the following (you will find links next to the code fragments that help to download full demo programs: save them on your computer and compile them according to the description in the page about \ref getsart How to start using LEMON):
25- First we give two examples that show how to instantiate a graph. The
26first one shows the methods that add nodes and edges, but one will
27usually use the second way which reads a graph from a stream (file).
[1511]28-# The following code fragment shows how to fill a graph with data. It creates a complete graph on 4 nodes. The type Listgraph is one of the LEMON graph types: the typedefs in the beginning are for convenience and we will suppose them later as well.
[1175]29 \code
30  typedef ListGraph Graph;
31  typedef Graph::NodeIt NodeIt;
33  Graph g;
35  for (int i = 0; i < 3; i++)
36    g.addNode();
38  for (NodeIt i(g); i!=INVALID; ++i)
39    for (NodeIt j(g); j!=INVALID; ++j)
40      if (i != j) g.addEdge(i, j);
41 \endcode
[1511]43See the whole program in file \ref
[1181]45If you want to read more on the LEMON graph structures and concepts, read the page about \ref graphs "graphs".
47-# The following code shows how to read a graph from a stream (e.g. a file). LEMON supports the DIMACS file format: it can read a graph instance from a file
[1511]48in that format (find the documentation of the DIMACS file format on the web).
50Graph g;
51std::ifstream f("graph.dim");
52readDimacs(f, g);
[1183]54One can also store network (graph+capacity on the edges) instances and other things in DIMACS format and use these in LEMON: to see the details read the documentation of the \ref dimacs.h "Dimacs file format reader".
57- If you want to solve some transportation problems in a network then
58you will want to find shortest paths between nodes of a graph. This is
59usually solved using Dijkstra's algorithm. A utility
60that solves this is  the \ref lemon::Dijkstra "LEMON Dijkstra class".
[1183]61The following code is a simple program using the \ref lemon::Dijkstra "LEMON
62Dijkstra class" and it also shows how to define a map on the edges (the length
67    typedef ListGraph Graph;
68    typedef Graph::Node Node;
69    typedef Graph::Edge Edge;
70    typedef Graph::EdgeMap<int> LengthMap;
72    Graph g;
74    //An example from Ahuja's book
76    Node s=g.addNode();
77    Node v2=g.addNode();
78    Node v3=g.addNode();
79    Node v4=g.addNode();
80    Node v5=g.addNode();
81    Node t=g.addNode();
83    Edge s_v2=g.addEdge(s, v2);
84    Edge s_v3=g.addEdge(s, v3);
85    Edge v2_v4=g.addEdge(v2, v4);
86    Edge v2_v5=g.addEdge(v2, v5);
87    Edge v3_v5=g.addEdge(v3, v5);
88    Edge v4_t=g.addEdge(v4, t);
89    Edge v5_t=g.addEdge(v5, t);
91    LengthMap len(g);
93    len.set(s_v2, 10);
94    len.set(s_v3, 10);
95    len.set(v2_v4, 5);
96    len.set(v2_v5, 8);
97    len.set(v3_v5, 5);
98    len.set(v4_t, 8);
99    len.set(v5_t, 8);
[1511]101    std::cout << "The id of s is " <<<< std::endl;
102    std::cout <<"The id of t is " <<<<"."<<std::endl;
104    std::cout << "Dijkstra algorithm test..." << std::endl;
106    Dijkstra<Graph, LengthMap> dijkstra_test(g,len);
111    std::cout << "The distance of node t from node s: " << dijkstra_test.dist(t)<<std::endl;
[1511]113    std::cout << "The shortest path from s to t goes through the following nodes" <<std::endl;
114 std::cout << " (the first one is t, the last one is s): "<<std::endl;
116    for (Node v=t;v != s; v=dijkstra_test.predNode(v)){
117        std::cout << << "<-";
118    }
119    std::cout << << std::endl; 
[1287]122See the whole program in \ref
124The first part of the code is self-explanatory: we build the graph and set the
125length values of the edges. Then we instantiate a member of the Dijkstra class
126and run the Dijkstra algorithm from node \c s. After this we read some of the
128You can do much more with the Dijkstra class, for example you can run it step
129by step and gain full control of the execution. For a detailed description, see the documentation of the \ref lemon::Dijkstra "LEMON Dijkstra class".
[1175]132- If you want to design a network and want to minimize the total length
133of wires then you might be looking for a <b>minimum spanning tree</b> in
134an undirected graph. This can be found using the Kruskal algorithm: the
135class \ref lemon::Kruskal "LEMON Kruskal class" does this job for you.
136The following code fragment shows an example:
[1511]138Ide Zsuzska fog irni!
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