1 | #region License Information
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2 |
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3 | /* HeuristicLab
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4 | * Copyright (C) 2002-2019 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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5 | *
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6 | * This file is part of HeuristicLab.
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7 | *
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8 | * HeuristicLab is free software: you can redistribute it and/or modify
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9 | * it under the terms of the GNU General Public License as published by
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10 | * the Free Software Foundation, either version 3 of the License, or
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11 | * (at your option) any later version.
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12 | *
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13 | * HeuristicLab is distributed in the hope that it will be useful,
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14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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16 | * GNU General Public License for more details.
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17 | *
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18 | * You should have received a copy of the GNU General Public License
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19 | * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
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20 | */
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21 |
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22 | #endregion
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23 |
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24 | using System;
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25 | using System.Collections.Generic;
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26 | using System.Linq;
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27 | namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
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28 | public static class GrammarUtils {
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29 | private static IEnumerable<ISymbol> GetTopmostSymbols(this ISymbolicExpressionGrammarBase grammar) {
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30 | // build parents list so we can find out the topmost symbol(s)
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31 | var parents = new Dictionary<ISymbol, List<ISymbol>>();
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32 | foreach (var symbol in grammar.Symbols.Where(x => grammar.GetMinimumSubtreeCount(x) > 0)) {
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33 | var minSubtreeCount = grammar.GetMinimumSubtreeCount(symbol);
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34 | for (int argIndex = 0; argIndex < minSubtreeCount; ++argIndex) {
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35 | foreach (var childSymbol in grammar.GetAllowedActiveSymbols(symbol, argIndex)) {
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36 | if (!parents.ContainsKey(childSymbol))
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37 | parents[childSymbol] = new List<ISymbol>();
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38 | parents[childSymbol].Add(symbol);
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39 | }
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40 | }
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41 | }
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42 | // the topmost symbols have no parents
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43 | return parents.Values.SelectMany(x => x).Distinct().Where(x => !parents.ContainsKey(x));
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44 | }
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45 |
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46 | private static IReadOnlyCollection<ISymbol> IterateBreadthReverse(this ISymbolicExpressionGrammarBase grammar, ISymbol topSymbol) {
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47 | // sort symbols in reverse breadth order (starting from the topSymbol)
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48 | // each symbol is visited only once (this avoids infinite recursion)
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49 | var symbols = new List<ISymbol> { topSymbol };
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50 | var visited = new HashSet<ISymbol> { topSymbol };
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51 | int i = 0;
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52 | while (i < symbols.Count) {
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53 | var symbol = symbols[i];
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54 | var minSubtreeCount = grammar.GetMinimumSubtreeCount(symbol);
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55 |
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56 | for (int argIndex = 0; argIndex < minSubtreeCount; ++argIndex) {
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57 | foreach (var childSymbol in grammar.GetAllowedActiveSymbols(symbol, argIndex)) {
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58 | if (grammar.GetMinimumSubtreeCount(childSymbol) == 0)
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59 | continue;
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60 |
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61 | if (visited.Add(childSymbol))
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62 | symbols.Add(childSymbol);
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63 | }
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64 | }
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65 | ++i;
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66 | }
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67 | symbols.Reverse();
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68 | return symbols;
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69 | }
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70 |
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71 | private static IEnumerable<ISymbol> GetAllowedActiveSymbols(this ISymbolicExpressionGrammarBase grammar, ISymbol symbol, int argIndex) {
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72 | return grammar.GetAllowedChildSymbols(symbol, argIndex).Where(s => s.InitialFrequency > 0);
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73 | }
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74 |
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75 | public static void CalculateMinimumExpressionLengths(ISymbolicExpressionGrammarBase grammar,
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76 | Dictionary<string, int> minimumExpressionLengths) {
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77 | minimumExpressionLengths.Clear();
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78 | //terminal symbols => minimum expression length = 1
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79 | foreach (var s in grammar.Symbols) {
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80 | if (grammar.GetMinimumSubtreeCount(s) == 0)
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81 | minimumExpressionLengths[s.Name] = 1;
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82 | else
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83 | minimumExpressionLengths[s.Name] = int.MaxValue;
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84 | }
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85 |
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86 | foreach (var topSymbol in grammar.GetTopmostSymbols()) {
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87 | // get all symbols below in reverse breadth order
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88 | // this way we ensure lengths are calculated bottom-up
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89 | var symbols = grammar.IterateBreadthReverse(topSymbol);
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90 | foreach (var symbol in symbols) {
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91 | long minLength = 1;
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92 | for (int argIndex = 0; argIndex < grammar.GetMinimumSubtreeCount(symbol); ++argIndex) {
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93 | long length = grammar.GetAllowedActiveSymbols(symbol, argIndex)
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94 | .Where(x => minimumExpressionLengths.ContainsKey(x.Name))
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95 | .Select(x => minimumExpressionLengths[x.Name]).DefaultIfEmpty(int.MaxValue).Min();
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96 | minLength += length;
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97 | }
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98 | int oldLength;
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99 | if (minimumExpressionLengths.TryGetValue(symbol.Name, out oldLength))
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100 | minLength = Math.Min(minLength, oldLength);
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101 | minimumExpressionLengths[symbol.Name] = (int)Math.Min(int.MaxValue, minLength);
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102 | }
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103 | // correction step for cycles
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104 | bool changed = true;
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105 | while (changed) {
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106 | changed = false;
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107 | foreach (var symbol in symbols) {
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108 | long minLength = Enumerable.Range(0, grammar.GetMinimumSubtreeCount(symbol))
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109 | .Sum(x => grammar.GetAllowedActiveSymbols(symbol, x)
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110 | .Select(s => (long)minimumExpressionLengths[s.Name]).DefaultIfEmpty(int.MaxValue).Min()) + 1;
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111 | if (minLength < minimumExpressionLengths[symbol.Name]) {
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112 | minimumExpressionLengths[symbol.Name] = (int)Math.Min(minLength, int.MaxValue);
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113 | changed = true;
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114 | }
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115 | }
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116 | }
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117 | }
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118 | }
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119 |
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120 | public static void CalculateMinimumExpressionDepth(ISymbolicExpressionGrammarBase grammar,
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121 | Dictionary<string, int> minimumExpressionDepths) {
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122 |
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123 | minimumExpressionDepths.Clear();
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124 | //terminal symbols => minimum expression depth = 1
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125 | foreach (var s in grammar.Symbols) {
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126 | if (grammar.GetMinimumSubtreeCount(s) == 0)
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127 | minimumExpressionDepths[s.Name] = 1;
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128 | else
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129 | minimumExpressionDepths[s.Name] = int.MaxValue;
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130 | }
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131 |
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132 | foreach (var topSymbol in grammar.GetTopmostSymbols()) {
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133 | // get all symbols below in reverse breadth order
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134 | // this way we ensure lengths are calculated bottom-up
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135 | var symbols = grammar.IterateBreadthReverse(topSymbol);
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136 | foreach (var symbol in symbols) {
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137 | long minDepth = -1;
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138 | for (int argIndex = 0; argIndex < grammar.GetMinimumSubtreeCount(symbol); ++argIndex) {
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139 | long depth = grammar.GetAllowedActiveSymbols(symbol, argIndex)
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140 | .Where(x => minimumExpressionDepths.ContainsKey(x.Name))
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141 | .Select(x => (long)minimumExpressionDepths[x.Name]).DefaultIfEmpty(int.MaxValue).Min() + 1;
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142 | minDepth = Math.Max(minDepth, depth);
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143 | }
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144 | int oldDepth;
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145 | if (minimumExpressionDepths.TryGetValue(symbol.Name, out oldDepth))
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146 | minDepth = Math.Min(minDepth, oldDepth);
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147 | minimumExpressionDepths[symbol.Name] = (int)Math.Min(int.MaxValue, minDepth);
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148 | }
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149 | // correction step for cycles
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150 | bool changed = true;
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151 | while (changed) {
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152 | changed = false;
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153 | foreach (var symbol in symbols) {
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154 | long minDepth = Enumerable.Range(0, grammar.GetMinimumSubtreeCount(symbol))
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155 | .Max(x => grammar.GetAllowedActiveSymbols(symbol, x)
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156 | .Select(s => (long)minimumExpressionDepths[s.Name]).DefaultIfEmpty(int.MaxValue).Min()) + 1;
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157 | if (minDepth < minimumExpressionDepths[symbol.Name]) {
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158 | minimumExpressionDepths[symbol.Name] = (int)Math.Min(minDepth, int.MaxValue);
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159 | changed = true;
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160 | }
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161 | }
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162 | }
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163 | }
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164 | }
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165 | }
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166 | }
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