138 lines
3.6 KiB
C#
138 lines
3.6 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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*
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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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{
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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 = {
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{ 2, 10, 50},
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{ 2, 10, 52},
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{50, 60, 3},
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{40, 60, 1}
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};
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//
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// Decision variables
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//
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IntVar[] open = solver.MakeIntVarArray(num_warehouses, 0, num_warehouses, "open");
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IntVar[,] ship = solver.MakeIntVarMatrix(num_customers, num_warehouses,
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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
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from w in WAREHOUSES
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select (demand[c]*distance[c,w]*ship[c,w])
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).ToArray().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 = solver.MakePhase(open.Concat(ship.Flatten()).ToArray(),
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Solver.CHOOSE_FIRST_UNBOUND,
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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].Value() + " ");
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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].Value()+ " ");
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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)
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{
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Solve();
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}
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}
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