88 lines
3.2 KiB
Java
88 lines
3.2 KiB
Java
// Copyright 2010-2022 Google LLC
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// [START program]
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// From Bradley, Hax, and Maganti, 'Applied Mathematical Programming', figure 8.1.
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package com.google.ortools.graph.samples;
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// [START import]
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import com.google.ortools.Loader;
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import com.google.ortools.graph.MinCostFlow;
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import com.google.ortools.graph.MinCostFlowBase;
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// [END import]
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/** Minimal MinCostFlow program. */
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public class SimpleMinCostFlowProgram {
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public static void main(String[] args) throws Exception {
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Loader.loadNativeLibraries();
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// [START solver]
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// Instantiate a SimpleMinCostFlow solver.
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MinCostFlow minCostFlow = new MinCostFlow();
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// [END solver]
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// [START data]
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// Define four parallel arrays: sources, destinations, capacities, and unit costs
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// between each pair. For instance, the arc from node 0 to node 1 has a
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// capacity of 15.
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// Problem taken From Taha's 'Introduction to Operations Research',
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// example 6.4-2.
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int[] startNodes = new int[] {0, 0, 1, 1, 1, 2, 2, 3, 4};
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int[] endNodes = new int[] {1, 2, 2, 3, 4, 3, 4, 4, 2};
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int[] capacities = new int[] {15, 8, 20, 4, 10, 15, 4, 20, 5};
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int[] unitCosts = new int[] {4, 4, 2, 2, 6, 1, 3, 2, 3};
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// Define an array of supplies at each node.
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int[] supplies = new int[] {20, 0, 0, -5, -15};
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// [END data]
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// [START constraints]
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// Add each arc.
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for (int i = 0; i < startNodes.length; ++i) {
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int arc = minCostFlow.addArcWithCapacityAndUnitCost(
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startNodes[i], endNodes[i], capacities[i], unitCosts[i]);
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if (arc != i) {
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throw new Exception("Internal error");
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}
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}
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// Add node supplies.
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for (int i = 0; i < supplies.length; ++i) {
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minCostFlow.setNodeSupply(i, supplies[i]);
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}
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// [END constraints]
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// [START solve]
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// Find the min cost flow.
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MinCostFlowBase.Status status = minCostFlow.solve();
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// [END solve]
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// [START print_solution]
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if (status == MinCostFlow.Status.OPTIMAL) {
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System.out.println("Minimum cost: " + minCostFlow.getOptimalCost());
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System.out.println();
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System.out.println(" Edge Flow / Capacity Cost");
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for (int i = 0; i < minCostFlow.getNumArcs(); ++i) {
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long cost = minCostFlow.getFlow(i) * minCostFlow.getUnitCost(i);
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System.out.println(minCostFlow.getTail(i) + " -> " + minCostFlow.getHead(i) + " "
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+ minCostFlow.getFlow(i) + " / " + minCostFlow.getCapacity(i) + " " + cost);
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}
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} else {
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System.out.println("Solving the min cost flow problem failed.");
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System.out.println("Solver status: " + status);
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}
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// [END print_solution]
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}
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private SimpleMinCostFlowProgram() {}
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}
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// [END program]
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