[12938] | 1 | #region License Information
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| 2 | /* HeuristicLab
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| 3 | * Copyright (C) 2002-2015 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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| 4 | *
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| 5 | * This file is part of HeuristicLab.
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| 6 | *
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| 7 | * HeuristicLab is free software: you can redistribute it and/or modify
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| 8 | * it under the terms of the GNU General Public License as published by
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| 9 | * the Free Software Foundation, either version 3 of the License, or
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| 10 | * (at your option) any later version.
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| 11 | *
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| 12 | * HeuristicLab is distributed in the hope that it will be useful,
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| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 15 | * GNU General Public License for more details.
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| 16 | *
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| 17 | * You should have received a copy of the GNU General Public License
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| 18 | * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
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| 19 | */
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| 20 | #endregion
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| 21 |
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| 22 | using System;
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| 23 | using System.Collections.Generic;
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| 24 | using System.Linq;
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| 25 | using HeuristicLab.Common;
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| 26 | using HeuristicLab.Core;
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| 27 | using HeuristicLab.Data;
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| 28 | using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
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| 29 | using HeuristicLab.Parameters;
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| 30 | using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
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| 31 |
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| 32 |
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| 33 | namespace HeuristicLab.Problems.GeneticProgramming.Boolean {
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| 34 | [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")]
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| 35 | [Creatable(CreatableAttribute.Categories.GeneticProgrammingProblems, Priority = 900)]
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[14711] | 36 | [StorableType("1394187F-9938-4214-B23C-E67FA599633C")]
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[12938] | 37 | public sealed class EvenParityProblem : SymbolicExpressionTreeProblem {
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| 38 |
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| 39 | #region parameter names
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| 40 | private const string NumberOfBitsParameterName = "NumberOfBits";
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| 41 | #endregion
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| 42 |
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| 43 | #region Parameter Properties
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| 44 | public IFixedValueParameter<IntValue> NumberOfBitsParameter {
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| 45 | get { return (IFixedValueParameter<IntValue>)Parameters[NumberOfBitsParameterName]; }
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| 46 | }
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| 47 | #endregion
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| 48 |
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| 49 | #region Properties
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| 50 | public int NumberOfBits {
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| 51 | get { return NumberOfBitsParameter.Value.Value; }
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| 52 | set { NumberOfBitsParameter.Value.Value = value; }
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| 53 | }
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| 54 | #endregion
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| 55 |
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| 56 | public override bool Maximization {
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| 57 | get { return true; }
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| 58 | }
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| 59 |
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[13269] | 60 | #region item cloning and persistence
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| 61 | // persistence
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| 62 | [StorableConstructor]
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| 63 | private EvenParityProblem(bool deserializing) : base(deserializing) { }
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| 64 | [StorableHook(HookType.AfterDeserialization)]
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| 65 | private void AfterDeserialization() {
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| 66 | RegisterEventHandlers();
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| 67 | }
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| 68 |
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| 69 | // cloning
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| 70 | private EvenParityProblem(EvenParityProblem original, Cloner cloner)
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| 71 | : base(original, cloner) {
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| 72 | RegisterEventHandlers();
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| 73 | }
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| 74 | public override IDeepCloneable Clone(Cloner cloner) {
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| 75 | return new EvenParityProblem(this, cloner);
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| 76 | }
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| 77 | #endregion
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| 78 |
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[12938] | 79 | public EvenParityProblem()
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| 80 | : base() {
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| 81 | Parameters.Add(new FixedValueParameter<IntValue>(NumberOfBitsParameterName, "The number of bits for the input parameter for the even parity function", new IntValue(4)));
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| 82 |
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| 83 | var g = new SimpleSymbolicExpressionGrammar(); // will be replaced in update grammar
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| 84 | Encoding = new SymbolicExpressionTreeEncoding(g, 100, 17);
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| 85 |
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| 86 | UpdateGrammar();
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| 87 | RegisterEventHandlers();
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| 88 | }
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| 89 |
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| 90 | private void UpdateGrammar() {
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| 91 | var g = new SimpleSymbolicExpressionGrammar();
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| 92 | g.AddSymbols(new[] { "AND", "OR", "NAND", "NOR" }, 2, 2); // see Koza, 1992, page 529 section 20.2 Symbolic Regression of Even-Parity Functions
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| 93 |
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| 94 | // add one terminal symbol for each bit
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| 95 | for (int i = 0; i < NumberOfBits; i++)
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| 96 | g.AddTerminalSymbol(string.Format("{0}", i));
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| 97 |
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| 98 | Encoding.Grammar = g;
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[13163] | 99 |
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| 100 | BestKnownQuality = Math.Pow(2, NumberOfBits); // this is a benchmark problem (the best achievable quality is known for a given number of bits)
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[12938] | 101 | }
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| 102 |
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| 103 |
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| 104 | public override double Evaluate(ISymbolicExpressionTree tree, IRandom random) {
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| 105 | if (NumberOfBits <= 0) throw new NotSupportedException("Number of bits must be larger than zero.");
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| 106 | if (NumberOfBits > 10) throw new NotSupportedException("Even parity does not support problems with number of bits > 10.");
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| 107 | var bs = Enumerable.Range(0, (int)Math.Pow(2, NumberOfBits));
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| 108 | var targets = bs.Select(b => CalcTarget(b, NumberOfBits));
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| 109 | var pred = Interpret(tree, bs);
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| 110 | return targets.Zip(pred, (t, p) => t == p ? 1 : 0).Sum(); // count number of correct predictions
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| 111 | }
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| 112 |
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| 113 | private static bool CalcTarget(int b, int numBits) {
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| 114 | bool res = GetBits(b, 0);
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| 115 | for (byte i = 1; i < numBits; i++)
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| 116 | res = res ^ GetBits(b, i); // XOR
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| 117 | return res;
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| 118 | }
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| 119 |
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| 120 | private static IEnumerable<bool> Interpret(ISymbolicExpressionTree tree, IEnumerable<int> bs) {
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| 121 | // skip programRoot and startSymbol
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| 122 | return InterpretRec(tree.Root.GetSubtree(0).GetSubtree(0), bs);
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| 123 | }
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| 124 |
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| 125 | private static IEnumerable<bool> InterpretRec(ISymbolicExpressionTreeNode node, IEnumerable<int> bs) {
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[13267] | 126 | Func<ISymbolicExpressionTreeNode, ISymbolicExpressionTreeNode, Func<bool, bool, bool>, IEnumerable<bool>> binaryEval =
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[12938] | 127 | (left, right, f) => InterpretRec(left, bs).Zip(InterpretRec(right, bs), f);
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| 128 |
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| 129 | switch (node.Symbol.Name) {
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[13269] | 130 | case "AND": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => x & y);
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| 131 | case "OR": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => x | y);
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[13267] | 132 | case "NAND": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => !(x & y));
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[13269] | 133 | case "NOR": return binaryEval(node.GetSubtree(0), node.GetSubtree(1), (x, y) => !(x | y));
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[12938] | 134 | default: {
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| 135 | byte bitPos;
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| 136 | if (byte.TryParse(node.Symbol.Name, out bitPos)) {
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| 137 | return bs.Select(b => GetBits(b, bitPos));
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| 138 | } else throw new NotSupportedException(string.Format("Found unexpected symbol {0}", node.Symbol.Name));
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| 139 | }
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| 140 | }
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| 141 | }
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| 142 |
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| 143 | private static bool GetBits(int b, byte bitPos) {
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| 144 | return (b & (1 << bitPos)) != 0;
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| 145 | }
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| 146 |
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| 147 | #region events
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| 148 | private void RegisterEventHandlers() {
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| 149 | NumberOfBitsParameter.Value.ValueChanged += (sender, args) => UpdateGrammar();
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| 150 | }
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| 151 | #endregion
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| 152 | }
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| 153 | }
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