+++ /dev/null
-/*
- * Created on Jul 6, 2007
- *
- * Copyright (c) 2007, the JUNG Project and the Regents of the University
- * of California
- * All rights reserved.
- *
- * This software is open-source under the BSD license; see either
- * "license.txt" or
- * http://jung.sourceforge.net/license.txt for a description.
- */
-package edu.uci.ics.jung.algorithms.scoring;
-
-import org.apache.commons.collections15.Transformer;
-
-import edu.uci.ics.jung.algorithms.scoring.util.UniformDegreeWeight;
-import edu.uci.ics.jung.graph.Hypergraph;
-
-/**
- * A generalization of PageRank that permits non-uniformly-distributed random jumps.
- * The 'vertex_priors' (that is, prior probabilities for each vertex) may be
- * thought of as the fraction of the total 'potential' that is assigned to that
- * vertex at each step out of the portion that is assigned according
- * to random jumps (this portion is specified by 'alpha').
- *
- * @see "Algorithms for Estimating Relative Importance in Graphs by Scott White and Padhraic Smyth, 2003"
- * @see PageRank
- */
-public class PageRankWithPriors<V, E>
- extends AbstractIterativeScorerWithPriors<V,E,Double>
-{
- /**
- * Maintains the amount of potential associated with vertices with no out-edges.
- */
- protected double disappearing_potential = 0.0;
-
- /**
- * Creates an instance with the specified graph, edge weights, vertex priors, and
- * 'random jump' probability (alpha).
- * @param graph the input graph
- * @param edge_weights the edge weights, denoting transition probabilities from source to destination
- * @param vertex_priors the prior probabilities for each vertex
- * @param alpha the probability of executing a 'random jump' at each step
- */
- public PageRankWithPriors(Hypergraph<V,E> graph,
- Transformer<E, ? extends Number> edge_weights,
- Transformer<V, Double> vertex_priors, double alpha)
- {
- super(graph, edge_weights, vertex_priors, alpha);
- }
-
- /**
- * Creates an instance with the specified graph, vertex priors, and
- * 'random jump' probability (alpha). The outgoing edge weights for each
- * vertex will be equal and sum to 1.
- * @param graph the input graph
- * @param vertex_priors the prior probabilities for each vertex
- * @param alpha the probability of executing a 'random jump' at each step
- */
- public PageRankWithPriors(Hypergraph<V,E> graph,
- Transformer<V, Double> vertex_priors, double alpha)
- {
- super(graph, vertex_priors, alpha);
- this.edge_weights = new UniformDegreeWeight<V,E>(graph);
- }
-
- /**
- * Updates the value for this vertex. Called by <code>step()</code>.
- */
- @Override
- public double update(V v)
- {
- collectDisappearingPotential(v);
-
- double v_input = 0;
- for (E e : graph.getInEdges(v))
- {
- // For graphs, the code below is equivalent to
-// V w = graph.getOpposite(v, e);
-// total_input += (getCurrentValue(w) * getEdgeWeight(w,e).doubleValue());
- // For hypergraphs, this divides the potential coming from w
- // by the number of vertices in the connecting edge e.
- int incident_count = getAdjustedIncidentCount(e);
- for (V w : graph.getIncidentVertices(e))
- {
- if (!w.equals(v) || hyperedges_are_self_loops)
- v_input += (getCurrentValue(w) *
- getEdgeWeight(w,e).doubleValue() / incident_count);
- }
- }
-
- // modify total_input according to alpha
- double new_value = alpha > 0 ?
- v_input * (1 - alpha) + getVertexPrior(v) * alpha :
- v_input;
- setOutputValue(v, new_value);
-
- return Math.abs(getCurrentValue(v) - new_value);
- }
-
- /**
- * Cleans up after each step. In this case that involves allocating the disappearing
- * potential (thus maintaining normalization of the scores) according to the vertex
- * probability priors, and then calling
- * <code>super.afterStep</code>.
- */
- @Override
- protected void afterStep()
- {
- // distribute disappearing potential according to priors
- if (disappearing_potential > 0)
- {
- for (V v : graph.getVertices())
- {
- setOutputValue(v, getOutputValue(v) +
- (1 - alpha) * (disappearing_potential * getVertexPrior(v)));
- }
- disappearing_potential = 0;
- }
-
- super.afterStep();
- }
-
- /**
- * Collects the "disappearing potential" associated with vertices that have
- * no outgoing edges. Vertices that have no outgoing edges do not directly
- * contribute to the scores of other vertices. These values are collected
- * at each step and then distributed across all vertices
- * as a part of the normalization process.
- */
- @Override
- protected void collectDisappearingPotential(V v)
- {
- if (graph.outDegree(v) == 0)
- {
- if (isDisconnectedGraphOK())
- disappearing_potential += getCurrentValue(v);
- else
- throw new IllegalArgumentException("Outdegree of " + v + " must be > 0");
- }
- }
-}