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source: branches/2521_ProblemRefactoring/HeuristicLab.Problems.GeneticProgramming/3.3/Boolean/EvenParityProblem.cs @ 17320

Last change on this file since 17320 was 17320, checked in by mkommend, 4 years ago

#2521: Added cancellation token to evaluate function of problems.

File size: 6.2 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) Heuristic and Evolutionary Algorithms Laboratory (HEAL)
4 *
5 * This file is part of HeuristicLab.
6 *
7 * HeuristicLab is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
11 *
12 * HeuristicLab is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
19 */
20#endregion
21
22using System;
23using System.Collections.Generic;
24using System.Linq;
25using System.Threading;
26using HEAL.Attic;
27using HeuristicLab.Common;
28using HeuristicLab.Core;
29using HeuristicLab.Data;
30using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
31using HeuristicLab.Parameters;
32
33
34namespace HeuristicLab.Problems.GeneticProgramming.Boolean {
35  [Item("Even Parity Problem", "The Boolean even parity genetic programming problem. See Koza, 1992, page 529 section 20.2 Symbolic Regression of Even-Parity Functions")]
36  [Creatable(CreatableAttribute.Categories.GeneticProgrammingProblems, Priority = 900)]
37  [StorableType("76D6001D-135F-45FB-BC79-061EDAEE33A9")]
38  public sealed class EvenParityProblem : SymbolicExpressionTreeProblem {
39
40    #region parameter names
41    private const string NumberOfBitsParameterName = "NumberOfBits";
42    #endregion
43
44    #region Parameter Properties
45    public IFixedValueParameter<IntValue> NumberOfBitsParameter {
46      get { return (IFixedValueParameter<IntValue>)Parameters[NumberOfBitsParameterName]; }
47    }
48    #endregion
49
50    #region Properties
51    public int NumberOfBits {
52      get { return NumberOfBitsParameter.Value.Value; }
53      set { NumberOfBitsParameter.Value.Value = value; }
54    }
55    #endregion
56
57    #region item cloning and persistence
58    // persistence
59    [StorableConstructor]
60    private EvenParityProblem(StorableConstructorFlag _) : base(_) { }
61    [StorableHook(HookType.AfterDeserialization)]
62    private void AfterDeserialization() {
63      RegisterEventHandlers();
64    }
65
66    // cloning
67    private EvenParityProblem(EvenParityProblem original, Cloner cloner)
68      : base(original, cloner) {
69      RegisterEventHandlers();
70    }
71    public override IDeepCloneable Clone(Cloner cloner) {
72      return new EvenParityProblem(this, cloner);
73    }
74    #endregion
75
76    public EvenParityProblem()
77      : base(new SymbolicExpressionTreeEncoding()) {
78      Maximization = true;
79      Parameters.Add(new FixedValueParameter<IntValue>(NumberOfBitsParameterName, "The number of bits for the input parameter for the even parity function", new IntValue(4)));
80
81      Encoding.TreeLength = 100;
82      Encoding.TreeDepth = 17;
83
84      UpdateGrammar();
85      RegisterEventHandlers();
86    }
87
88    private void UpdateGrammar() {
89      var g = new SimpleSymbolicExpressionGrammar();
90      g.AddSymbols(new[] { "AND", "OR", "NAND", "NOR" }, 2, 2); // see Koza, 1992, page 529 section 20.2 Symbolic Regression of Even-Parity Functions
91
92      // add one terminal symbol for each bit
93      for (int i = 0; i < NumberOfBits; i++)
94        g.AddTerminalSymbol(string.Format("{0}", i));
95
96      Encoding.GrammarParameter.ReadOnly = false;
97      Encoding.Grammar = g;
98      Encoding.GrammarParameter.ReadOnly = true;
99
100      BestKnownQualityParameter.ReadOnly = false;
101      BestKnownQuality = Math.Pow(2, NumberOfBits); // this is a benchmark problem (the best achievable quality is known for a given number of bits)
102      BestKnownQualityParameter.ReadOnly = true;
103    }
104
105
106    public override double Evaluate(ISymbolicExpressionTree tree, IRandom random, CancellationToken cancellationToken) {
107      if (NumberOfBits <= 0) throw new NotSupportedException("Number of bits must be larger than zero.");
108      if (NumberOfBits > 10) throw new NotSupportedException("Even parity does not support problems with number of bits > 10.");
109      var bs = Enumerable.Range(0, (int)Math.Pow(2, NumberOfBits));
110      var targets = bs.Select(b => CalcTarget(b, NumberOfBits));
111      var pred = Interpret(tree, bs);
112      return targets.Zip(pred, (t, p) => t == p ? 1 : 0).Sum(); // count number of correct predictions
113    }
114
115    private static bool CalcTarget(int b, int numBits) {
116      bool res = GetBits(b, 0);
117      for (byte i = 1; i < numBits; i++)
118        res = res ^ GetBits(b, i); // XOR
119      return res;
120    }
121
122    private static IEnumerable<bool> Interpret(ISymbolicExpressionTree tree, IEnumerable<int> bs) {
123      // skip programRoot and startSymbol
124      return InterpretRec(tree.Root.GetSubtree(0).GetSubtree(0), bs);
125    }
126
127    private static IEnumerable<bool> InterpretRec(ISymbolicExpressionTreeNode node, IEnumerable<int> bs) {
128      Func<ISymbolicExpressionTreeNode, ISymbolicExpressionTreeNode, Func<bool, bool, bool>, IEnumerable<bool>> binaryEval =
129        (left, right, f) => InterpretRec(left, bs).Zip(InterpretRec(right, bs), f);
130
131      switch (node.Symbol.Name) {
132        case "AND": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => x & y);
133        case "OR": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => x | y);
134        case "NAND": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => !(x & y));
135        case "NOR": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => !(x | y));
136        default: {
137            byte bitPos;
138            if (byte.TryParse(node.Symbol.Name, out bitPos)) {
139              return bs.Select(b => GetBits(b, bitPos));
140            } else throw new NotSupportedException(string.Format("Found unexpected symbol {0}", node.Symbol.Name));
141          }
142      }
143    }
144
145    private static bool GetBits(int b, byte bitPos) {
146      return (b & (1 << bitPos)) != 0;
147    }
148
149    #region events
150    private void RegisterEventHandlers() {
151      NumberOfBitsParameter.Value.ValueChanged += (sender, args) => UpdateGrammar();
152    }
153    #endregion
154  }
155}
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