129 lines
3.7 KiB
C#
129 lines
3.7 KiB
C#
//
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// Copyright 2012 Hakan Kjellerstrand
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//
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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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using System;
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using System.Collections;
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using System.Collections.Generic;
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using System.Linq;
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using Google.OrTools.ConstraintSolver;
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public class PMedian {
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/**
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*
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* P-median problem.
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*
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* Model and data from the OPL Manual, which describes the problem:
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* """
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* The P-Median problem is a well known problem in Operations Research.
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* The problem can be stated very simply, like this: given a set of customers
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* with known amounts of demand, a set of candidate locations for warehouses,
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* and the distance between each pair of customer-warehouse, choose P
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* warehouses to open that minimize the demand-weighted distance of serving
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* all customers from those P warehouses.
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* """
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*
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* Also see http://www.hakank.org/or-tools/p_median.py
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*
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*/
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private static void Solve() {
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Solver solver = new Solver("PMedian");
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//
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// Data
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//
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int p = 2;
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int num_customers = 4;
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IEnumerable<int> CUSTOMERS = Enumerable.Range(0, num_customers);
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int num_warehouses = 3;
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IEnumerable<int> WAREHOUSES = Enumerable.Range(0, num_warehouses);
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int[] demand = {100, 80, 80, 70};
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int[, ] distance = {{2, 10, 50}, {2, 10, 52}, {50, 60, 3}, {40, 60, 1}};
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//
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// Decision variables
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//
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IntVar[] open =
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solver.MakeIntVarArray(num_warehouses, 0, num_warehouses, "open");
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IntVar[, ] ship =
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solver.MakeIntVarMatrix(num_customers, num_warehouses, 0, 1, "ship");
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IntVar z = solver.MakeIntVar(0, 1000, "z");
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//
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// Constraints
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//
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solver.Add((from c in CUSTOMERS from w in WAREHOUSES select(
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demand[c] * distance[c, w] * ship[c, w]))
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.ToArray()
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.Sum() == z);
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solver.Add(open.Sum() == p);
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foreach (int c in CUSTOMERS) {
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foreach (int w in WAREHOUSES) {
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solver.Add(ship[c, w] <= open[w]);
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}
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solver.Add((from w in WAREHOUSES select ship[c, w]).ToArray().Sum() == 1);
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}
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//
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// Objective
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//
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OptimizeVar obj = z.Minimize(1);
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//
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// Search
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//
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DecisionBuilder db =
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solver.MakePhase(open.Concat(ship.Flatten()).ToArray(),
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Solver.CHOOSE_FIRST_UNBOUND, Solver.ASSIGN_MIN_VALUE);
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solver.NewSearch(db, obj);
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while (solver.NextSolution()) {
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Console.WriteLine("z: {0}", z.Value());
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Console.Write("open:");
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foreach (int w in WAREHOUSES) {
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Console.Write(open [w]
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.Value() +
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" ");
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}
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Console.WriteLine();
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foreach (int c in CUSTOMERS) {
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foreach (int w in WAREHOUSES) {
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Console.Write(ship [c, w]
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.Value() +
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" ");
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}
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Console.WriteLine();
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}
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Console.WriteLine();
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}
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Console.WriteLine("\nSolutions: {0}", solver.Solutions());
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Console.WriteLine("WallTime: {0}ms", solver.WallTime());
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Console.WriteLine("Failures: {0}", solver.Failures());
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Console.WriteLine("Branches: {0} ", solver.Branches());
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solver.EndSearch();
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}
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public static void Main(String[] args) { Solve(); }
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}
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