Ligra currently supports four different vertex types.
symmetricVertexasymmetricVertexcompressedSymmetricVertexcompressedAsymmetricVertexThe framework automatically picks the correct vertex type to use based on the command line flag a user supplies when running the application.
-c is supplied, then the graph is assumed to be compressed and
one of the compressed vertex types is selected. -s is supplied, the graph is assumed to be symmetric (undirected)
and a symmetric vertex type is selected. Otherwise, an asymmetric vertex type is selected. Certain applications, like PageRank, must work on both directed and undirected graphs, and therefore must do things like only iterating over out-edges, etc. In order to maximize code-reuse and not have different PageRank applications for directed and undirected graphs Ligra ensures that all four vertex types (implicitly) ascribe to the same interface.
intE getInNeighbor(intT j) : Returns the j'th in-neighbor of the vertex. intE getOutNeighbor(intT j) : Returns the j'th out-neighbor of the vertex. intE getInWeight(intT j) : Returns the weight of the edge from the j'th in-neighbor.intE getOutWeight(intT j) : Returns the weight of the edge to the j'th out-neighbor.intE getInDegree() : Returns the number of in-neighbors of the vertex.intE getOutDegree() : Returns the number of out-neighbors of the vertex.