BGL defines the concept BidirectionalGraph as follows:
The BidirectionalGraph concept refines IncidenceGraph and adds the requirement for efficient access to the in-edges of each vertex. This concept is separated from IncidenceGraph because, for directed graphs, efficient access to in-edges typically requires more storage space, and many algorithms do not require access to in-edges. For undirected graphs, this is not an issue; because the in_edges() and out_edges() functions are the same, they both return the edges incident to the vertex.
Returns the number of in-edges plus out-edges (for directed graphs) or the number of incident edges (for undirected graphs) of vertex v.
# File lib/rgl/bidirectional.rb, line 36 def degree (v) in_degree(v) + out_degree(v) end
Iterator providing access to the in-edges (for directed graphs) or incident edges (for undirected graphs) of vertex v. For both directed and undirected graphs, the target of an out-edge is required to be vertex v and the source is required to be a vertex that is adjacent to v.
# File lib/rgl/bidirectional.rb, line 21 def each_in_neighbor (v) raise NotImplementedError yield u end
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