Wrapper Classes for Graphs
[Graph Structures]


Detailed Description

The main parts of LEMON are the different graph structures, generic graph algorithms, graph concepts which couple these, and graph wrappers. While the previous ones are more or less clear, the latter notion needs further explanation. Graph wrappers are graph classes which serve for considering graph structures in different ways. A short example makes the notion much clearer. Suppose that we have an instance g of a directed graph type say ListGraph and an algorithm
 template<typename Graph> int algorithm(const Graph&); 
is needed to run on the reversely oriented graph. It may be expensive (in time or in memory usage) to copy g with the reverse orientation. Thus, a wrapper class
 template<typename Graph> class RevGraphWrapper; 
is used. The code looks as follows
      ListGraph g;
      RevGraphWrapper<ListGraph> rgw(g);
      int result=algorithm(rgw);
After running the algorithm, the original graph g remains untouched. Thus the graph wrapper used above is to consider the original graph with reverse orientation. This techniques gives rise to an elegant code, and based on stable graph wrappers, complex algorithms can be implemented easily. In flow, circulation and bipartite matching problems, the residual graph is of particular importance. Combining a wrapper implementing this, shortest path algorithms and minimum mean cycle algorithms, a range of weighted and cardinality optimization algorithms can be obtained. For lack of space, for other examples, the interested user is referred to the detailed documentation of graph wrappers. The behavior of graph wrappers can be very different. Some of them keep capabilities of the original graph while in other cases this would be meaningless. This means that the concepts that they are a model of depend on the graph wrapper, and the wrapped graph(s). If an edge of rgw is deleted, this is carried out by deleting the corresponding edge of g. But for a residual graph, this operation has no sense. Let we stand one more example here to simplify your work. wrapper class
 template<typename Graph> class RevGraphWrapper; 
has constructor RevGraphWrapper(Graph& _g). This means that in a situation, when a const ListGraph& reference to a graph is given, then it have to be instantiated with Graph=const ListGraph.
      int algorithm1(const ListGraph& g) {
        RevGraphWrapper<const ListGraph> rgw(g);
        return algorithm2(rgw);
      }


Files

file  graph_wrapper.h
 Several graph wrappers.

Classes

class  GraphWrapper
 Base type for the Graph Wrappers. More...
class  RevGraphWrapper
 A graph wrapper which reverses the orientation of the edges. More...
class  SubGraphWrapper
 A graph wrapper for hiding nodes and edges from a graph. More...
class  SubBidirGraphWrapper
 A wrapper for composing a subgraph of a bidirected graph made from a directed one. More...
class  BidirGraphWrapper
 A wrapper for composing bidirected graph from a directed one. More...
class  BidirGraph
 A bidirected graph template. More...
class  ResGraphWrapper
 A wrapper for composing the residual graph for directed flow and circulation problems. More...
class  ErasingFirstGraphWrapper
 For blocking flows. More...


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