/*
* Created on Jul 15, 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 java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import org.apache.commons.collections15.Transformer;
import edu.uci.ics.jung.algorithms.scoring.util.UniformDegreeWeight;
import edu.uci.ics.jung.graph.Hypergraph;
/**
* Assigns scores to vertices according to their 'voltage' in an approximate
* solution to the Kirchoff equations. This is accomplished by tying "source"
* vertices to specified positive voltages, "sink" vertices to 0 V, and
* iteratively updating the voltage of each other vertex to the (weighted)
* average of the voltages of its neighbors.
*
*
The resultant voltages will all be in the range [0, max]
* where max
is the largest voltage of any source vertex (in the
* absence of negative source voltages; see below).
*
*
A few notes about this algorithm's interpretation of the graph data:
*
* Higher edge weights are interpreted as indicative of greater
* influence/effect than lower edge weights.
* Negative edge weights (and negative "source" voltages) invalidate
* the interpretation of the resultant values as voltages. However, this
* algorithm will not reject graphs with negative edge weights or source voltages.
* Parallel edges are equivalent to a single edge whose weight is the
* sum of the weights on the parallel edges.
* Current flows along undirected edges in both directions,
* but only flows along directed edges in the direction of the edge.
*
*
*/
public class VoltageScorer extends AbstractIterativeScorer
implements VertexScorer
{
protected Map source_voltages;
protected Collection sinks;
/**
* Creates an instance with the specified graph, edge weights, source voltages,
* and sinks.
* @param g the input graph
* @param edge_weights the edge weights, representing conductivity
* @param source_voltages the (fixed) voltage for each source
* @param sinks the vertices whose voltages are tied to 0
*/
public VoltageScorer(Hypergraph g, Transformer edge_weights,
Map source_voltages, Collection sinks)
{
super(g, edge_weights);
this.source_voltages = source_voltages;
this.sinks = sinks;
initialize();
}
/**
* Creates an instance with the specified graph, edge weights, source vertices
* (each of whose 'voltages' are tied to 1), and sinks.
* @param g the input graph
* @param edge_weights the edge weights, representing conductivity
* @param sources the vertices whose voltages are tied to 1
* @param sinks the vertices whose voltages are tied to 0
*/
public VoltageScorer(Hypergraph g, Transformer edge_weights,
Collection sources, Collection sinks)
{
super(g, edge_weights);
Map unit_voltages = new HashMap();
for(V v : sources)
unit_voltages.put(v, new Double(1.0));
this.source_voltages = unit_voltages;
this.sinks = sinks;
initialize();
}
/**
* Creates an instance with the specified graph, source vertices
* (each of whose 'voltages' are tied to 1), and sinks.
* The outgoing edges for each vertex are assigned
* weights that sum to 1.
* @param g the input graph
* @param sources the vertices whose voltages are tied to 1
* @param sinks the vertices whose voltages are tied to 0
*/
public VoltageScorer(Hypergraph g, Collection sources, Collection sinks)
{
super(g);
Map unit_voltages = new HashMap();
for(V v : sources)
unit_voltages.put(v, new Double(1.0));
this.source_voltages = unit_voltages;
this.sinks = sinks;
initialize();
}
/**
* Creates an instance with the specified graph, source voltages,
* and sinks. The outgoing edges for each vertex are assigned
* weights that sum to 1.
* @param g the input graph
* @param source_voltages the (fixed) voltage for each source
* @param sinks the vertices whose voltages are tied to 0
*/
public VoltageScorer(Hypergraph g, Map source_voltages,
Collection sinks)
{
super(g);
this.source_voltages = source_voltages;
this.sinks = sinks;
this.edge_weights = new UniformDegreeWeight(g);
initialize();
}
/**
* Creates an instance with the specified graph, edge weights, source, and
* sink. The source vertex voltage is tied to 1.
* @param g the input graph
* @param edge_weights the edge weights, representing conductivity
* @param source the vertex whose voltage is tied to 1
* @param sink the vertex whose voltage is tied to 0
*/
public VoltageScorer(Hypergraph g, Transformer edge_weights,
V source, V sink)
{
this(g, edge_weights, Collections.singletonMap(source, 1.0), Collections.singletonList(sink));
initialize();
}
/**
* Creates an instance with the specified graph, edge weights, source, and
* sink. The source vertex voltage is tied to 1.
* The outgoing edges for each vertex are assigned
* weights that sum to 1.
* @param g the input graph
* @param source the vertex whose voltage is tied to 1
* @param sink the vertex whose voltage is tied to 0
*/
public VoltageScorer(Hypergraph g, V source, V sink)
{
this(g, Collections.singletonMap(source, 1.0), Collections.singletonList(sink));
initialize();
}
/**
* Initializes the state of this instance.
*/
@Override
public void initialize()
{
super.initialize();
// sanity check
if (source_voltages.isEmpty() || sinks.isEmpty())
throw new IllegalArgumentException("Both sources and sinks (grounds) must be defined");
if (source_voltages.size() + sinks.size() > graph.getVertexCount())
throw new IllegalArgumentException("Source/sink sets overlap, or contain vertices not in graph");
for (Map.Entry entry : source_voltages.entrySet())
{
V v = entry.getKey();
if (sinks.contains(v))
throw new IllegalArgumentException("Vertex " + v + " is incorrectly specified as both source and sink");
double value = entry.getValue().doubleValue();
if (value <= 0)
throw new IllegalArgumentException("Source vertex " + v + " has negative voltage");
}
// set up initial voltages
for (V v : graph.getVertices())
{
if (source_voltages.containsKey(v))
setOutputValue(v, source_voltages.get(v).doubleValue());
else
setOutputValue(v, 0.0);
}
}
/**
* @see edu.uci.ics.jung.algorithms.scoring.AbstractIterativeScorer#update(Object)
*/
@Override
public double update(V v)
{
// if it's a voltage source or sink, we're done
Number source_volts = source_voltages.get(v);
if (source_volts != null)
{
setOutputValue(v, source_volts.doubleValue());
return 0.0;
}
if (sinks.contains(v))
{
setOutputValue(v, 0.0);
return 0.0;
}
Collection edges = graph.getInEdges(v);
double voltage_sum = 0;
double weight_sum = 0;
for (E e: edges)
{
int incident_count = getAdjustedIncidentCount(e);
for (V w : graph.getIncidentVertices(e))
{
if (!w.equals(v) || hyperedges_are_self_loops)
{
double weight = getEdgeWeight(w,e).doubleValue() / incident_count;
voltage_sum += getCurrentValue(w).doubleValue() * weight;
weight_sum += weight;
}
}
// V w = graph.getOpposite(v, e);
// double weight = getEdgeWeight(w,e).doubleValue();
// voltage_sum += getCurrentValue(w).doubleValue() * weight;
// weight_sum += weight;
}
// if either is 0, new value is 0
if (voltage_sum == 0 || weight_sum == 0)
{
setOutputValue(v, 0.0);
return getCurrentValue(v).doubleValue();
}
setOutputValue(v, voltage_sum / weight_sum);
return Math.abs(getCurrentValue(v).doubleValue() - voltage_sum / weight_sum);
}
}