This function implements algorithm 4.2.1 of Gross and Yellen. The input is a graph and a node to start from. It returns a standard vertex labeling of graph. This is a vector with elements corresponding to the nodes of graph and with values that correspond to point in the depth first search the node is visited.
The MultiGraph class represents a single node set and a set of edge sets. Each edge set is either directed or undirected. We can think of an edge in a MultiGraph as a 4-tuple (from-node, to-node, edge-type, weight), where the edge-type field in the tuple identifies the edge set, the weight is a numeric value, and the order of the nodes only matters in the case of a directed edge set. Unlike some of the graph representations, self-loops are allowed (from-node == to-node).
This generic function takes an object that inherits from the graph class and a node in that graph and returns a vector containing information about all other nodes that are accessible from the given node. The methods are vectorized so that index can be a vector.
adj-methods
(Package: graph) :
Methods for finding the adjacency list for selected nodes.
This generic function takes an object that inherits from the graph class and a node in that graph and returns a vector containing information about all other nodes that are adjacent to the given node. This means that they are joined to the given node by an edge. The accessibility list, acc is the list of all nodes that can be reached from a specified node.
providing 
.