Subclassing edges and vertices

For particular applications it is convenient to subclass Edge or Vertex. When subclassing vertices it is important to subclass UVertex if the graph is undirected and DVertex if the graph is directed.

For example:

class PGVertex(pgraph.UVertex):

    nvertices = 0 # count of PGVertex instances

    def __init__(self, type, **kwargs):
        super().__init__(**kwargs)  # superclass initialiser
        self.type = type  # pose graph vertex type
        self.index = PGVertex.nvertices # pose graph vertex id
        PGVertex.nvertices += 1

class PGEdge(pgraph.Edge):
    def __init__(self, v1, v2, mean, info):
        super().__init__(v1, v2)  # superclass initialiser
        self.mean = mean  # edge cost
        self.info = info  # edge information matrix

    ## methods on edges
    def linear_factors(self):
        #computes the Taylor expansion of the error function of the k_th edge
        ...