public boolean equals(Object obj) {
ReachabilityEdge edge = (ReachabilityEdge) obj;
if (!(edge.getFrom().equals(this.getFrom()))) {
return false;
}
return edge.getTo().equals(this.getTo());
}
/**
* Returns the set of nodes reachable from the given set of initial nodes in the given graph
* according to the criteria in the given legal pairs object.
*
* <p>A variable V is reachable from initialNodes iff for some variable X in initialNodes thers is
* a path U [X, Y1, ..., V] such that legalPairs.isLegalFirstNode(X, Y1) and for each [H1, H2, H3]
* as subpaths of U, legalPairs.isLegalPairs(H1, H2, H3).
*
* <p>The algorithm used is a variant of Algorithm 1 from Geiger, Verma, & Pearl (1990).
*
* @param initialNodes The nodes that reachability paths start from.
* @param legalPairs Specifies initial edges (given initial nodes) and legal edge pairs.
* @param c a set of vertices (intuitively, the set of variables to be conditioned on.
* @param d a set of vertices (intuitively to be used in tests of legality, for example, the set
* of ancestors of c).
* @param graph the graph with respect to which reachability is determined.
*/
public static Set<Node> getReachableNodes(
List<Node> initialNodes, LegalPairs legalPairs, List<Node> c, List<Node> d, Graph graph) {
HashSet<Node> reachable = new HashSet<Node>();
MultiKeyMap visited = new MultiKeyMap();
List<ReachabilityEdge> nextEdges = new LinkedList<ReachabilityEdge>();
for (Node x : initialNodes) {
List<Node> adjX = graph.getAdjacentNodes(x);
for (Node y : adjX) {
if (legalPairs.isLegalFirstEdge(x, y)) {
reachable.add(y);
nextEdges.add(new ReachabilityEdge(x, y));
visited.put(x, y, Boolean.TRUE);
}
}
}
while (nextEdges.size() > 0) {
List<ReachabilityEdge> currEdges = nextEdges;
nextEdges = new LinkedList<ReachabilityEdge>();
for (ReachabilityEdge edge : currEdges) {
Node x = edge.getFrom();
Node y = edge.getTo();
List<Node> adjY = graph.getAdjacentNodes(y);
for (Node z : adjY) {
if ((visited.get(y, z)) == Boolean.TRUE) {
continue;
}
if (legalPairs.isLegalPair(x, y, z, c, d)) {
reachable.add(z);
nextEdges.add(new ReachabilityEdge(y, z));
visited.put(y, z, Boolean.TRUE);
}
}
}
}
return reachable;
}