org.matsim.contrib.drt.optimizer.rebalancing.mincostflow.TransportProblem.java Source code

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Here is the source code for org.matsim.contrib.drt.optimizer.rebalancing.mincostflow.TransportProblem.java

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/* *********************************************************************** *
 * project: org.matsim.*
 * *********************************************************************** *
 *                                                                         *
 * copyright       : (C) 2018 by the members listed in the COPYING,        *
 *                   LICENSE and WARRANTY file.                            *
 * email           : info at matsim dot org                                *
 *                                                                         *
 * *********************************************************************** *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *   See also COPYING, LICENSE and WARRANTY file                           *
 *                                                                         *
 * *********************************************************************** */

package org.matsim.contrib.drt.optimizer.rebalancing.mincostflow;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.ToIntBiFunction;
import java.util.stream.Stream;

import org.apache.commons.lang3.tuple.Pair;
import org.apache.commons.lang3.tuple.Triple;

import graphs.flows.MinCostFlow;
import graphs.flows.MinCostFlow.Edge;

/**
 * @author michalm
 */
public class TransportProblem<P, C> {
    private final ToIntBiFunction<P, C> costFunction;

    public TransportProblem(ToIntBiFunction<P, C> costFunction) {
        this.costFunction = costFunction;
    }

    public List<Triple<P, C, Integer>> solve(List<Pair<P, Integer>> supply, List<Pair<C, Integer>> demand) {
        final int P = supply.size();
        final int C = demand.size();
        final int N = P + C + 2;

        // N nodes, which indices are:
        // 0 - source
        // 1..P - producers 1..P
        // P+1..P+C - consumers 1..C
        // P+C+1 - sink

        @SuppressWarnings("unchecked")
        List<Edge>[] graph = Stream.generate(ArrayList::new).limit(N).toArray(List[]::new);

        // source -> producers
        int totalSupply = 0;
        for (int i = 0; i < P; i++) {
            int supplyValue = supply.get(i).getValue();
            MinCostFlow.addEdge(graph, 0, 1 + i, supplyValue, 0);
            totalSupply += supplyValue;
        }

        // producers --> consumers
        for (int i = 0; i < P; i++) {
            Pair<P, Integer> producer = supply.get(i);
            for (int j = 0; j < C; j++) {
                Pair<C, Integer> consumer = demand.get(j);
                int capacity = Math.min(producer.getValue(), consumer.getValue());
                int cost = costFunction.applyAsInt(producer.getKey(), consumer.getKey());
                MinCostFlow.addEdge(graph, 1 + i, 1 + P + j, capacity, cost);
            }
        }

        // consumers -> sink
        int totalDemand = 0;
        for (int j = 0; j < C; j++) {
            int demandValue = demand.get(j).getValue();
            MinCostFlow.addEdge(graph, 1 + P + j, N - 1, demandValue, 0);
            totalDemand += demandValue;
        }

        // solve min cost flow problem
        int[] result = MinCostFlow.minCostFlow(graph, 0, N - 1, Math.min(totalSupply, totalDemand), false);
        if (result[0] == 0) {
            return Collections.emptyList();
        }

        // extract flows
        List<Triple<P, C, Integer>> flows = new ArrayList<>();
        for (int i = 0; i < P; i++) {
            P from = supply.get(i).getKey();
            for (Edge e : graph[1 + i]) {
                int flow = e.getFlow();
                if (flow > 0) {
                    int j = e.getTo() - (1 + P);
                    C to = demand.get(j).getKey();
                    flows.add(Triple.of(from, to, flow));
                }
            }
        }
        return flows;
    }
}