LBGRemainingWeightHeuristic.java

/* This program is free software: you can redistribute it and/or
 modify it under the terms of the GNU Lesser General Public License
 as published by the Free Software Foundation, either version 3 of
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package org.opentripplanner.routing.algorithm.strategies;

import java.util.HashMap;

import org.opentripplanner.common.model.T2;
import org.opentripplanner.routing.core.LowerBoundGraph;
import org.opentripplanner.routing.core.State;
import org.opentripplanner.routing.core.RoutingRequest;
import org.opentripplanner.routing.graph.Graph;
import org.opentripplanner.routing.graph.Vertex;
import org.opentripplanner.routing.location.StreetLocation;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Intended primarily for testing of and experimentation with heuristics based on the triangle inequality and metric embeddings.
 * 
 * A heuristic that performs a single-source / all destinations shortest path search in a weighted, directed graph whose shortest path metric is a
 * lower bound on path weight in our main, time-dependent graph.
 * 
 * @author andrewbyrd
 */
public class LBGRemainingWeightHeuristic implements RemainingWeightHeuristic {

    private static final long serialVersionUID = 20110901L;

    private static Logger LOG = LoggerFactory.getLogger(LBGRemainingWeightHeuristic.class);

    private static HashMap<GraphAndDirection, LowerBoundGraph> lbgCache = new HashMap<GraphAndDirection, LowerBoundGraph>();

    LowerBoundGraph lbg;

    Vertex target;

    double[] weights;

    public LBGRemainingWeightHeuristic(Graph g, RoutingRequest opt) {
        GraphAndDirection key = new GraphAndDirection(g, opt.isArriveBy());
        this.lbg = lbgCache.get(key);
        if (this.lbg == null) {
            LOG.debug("no lower bound graph found for: {}", key);
            LOG.debug("BEGIN Making lower bound graph");
            if (opt.isArriveBy())
                this.lbg = new LowerBoundGraph(g, LowerBoundGraph.OUTGOING);
            else
                this.lbg = new LowerBoundGraph(g, LowerBoundGraph.INCOMING);
            LOG.debug("END   Making lower bound graph");
            lbgCache.put(key, this.lbg);
        } else {
            LOG.debug("reusing cached lower bound graph found for: {}", key);
        }
    }

    @Override
    public void initialize(State s, Vertex target) {
        recalculate(target);
    }

    @Override
    public double computeForwardWeight(State s, Vertex target) {
        return computeReverseWeight(s, target);
    }

    @Override
    public double computeReverseWeight(State s, Vertex target) {
        int index = s.getVertex().getIndex();
        if (index < weights.length) {
            double h = weights[index];
            // System.out.printf("h=%f at %s\n", h, s.getVertex());
            return h == Double.POSITIVE_INFINITY ? 0 : h;
        } else
            return 0;
    }

    private void recalculate(Vertex target) {
        if (target != this.target) {
            this.target = target;
            if (target instanceof StreetLocation)
                this.weights = lbg.sssp((StreetLocation) target);
            else
                this.weights = lbg.sssp(target);
        }
    }

    private static class GraphAndDirection extends T2<Graph, Boolean> {
        private static final long serialVersionUID = 20110901L;

        public GraphAndDirection(Graph g, Boolean i) {
            super(g, i);
        }
    }

    @Override
    public void reset() {}
    
    @Override
    public void abort() {}
}