[645] | 1 | #region License Information
|
---|
| 2 | /* HeuristicLab
|
---|
| 3 | * Copyright (C) 2002-2008 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 |
|
---|
| 22 | using HeuristicLab.Core;
|
---|
| 23 | using HeuristicLab.Data;
|
---|
| 24 | using HeuristicLab.Random;
|
---|
[2730] | 25 | using System;
|
---|
[3223] | 26 | using System.Linq;
|
---|
| 27 | using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
|
---|
| 28 | using System.Collections.Generic;
|
---|
[645] | 29 |
|
---|
[3223] | 30 | namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
|
---|
| 31 | [StorableClass]
|
---|
| 32 | [Item("ProbabilisticTreeCreator", "An operator that creates new symbolic expression trees with uniformly distributed size")]
|
---|
| 33 | public class ProbabilisticTreeCreator : SymbolicExpressionTreeCreator {
|
---|
[645] | 34 | public ProbabilisticTreeCreator()
|
---|
| 35 | : base() {
|
---|
| 36 | }
|
---|
| 37 |
|
---|
[3223] | 38 | protected override SymbolicExpressionTree Create(IRandom random, ISymbolicExpressionGrammar grammar, IntValue maxTreeSize, IntValue maxTreeHeight) {
|
---|
| 39 | return Apply(random, grammar, maxTreeSize.Value, maxTreeHeight.Value);
|
---|
[2447] | 40 | }
|
---|
| 41 |
|
---|
[3223] | 42 | public SymbolicExpressionTree Apply(IRandom random, ISymbolicExpressionGrammar grammar, int maxTreeSize, int maxTreeHeight) {
|
---|
| 43 | // tree size is limited by the grammar and by the explicit size constraints
|
---|
| 44 | int allowedMinSize = grammar.MinimalExpressionLength(grammar.StartSymbol);
|
---|
| 45 | int allowedMaxSize = Math.Min(maxTreeSize, grammar.MaximalExpressionLength(grammar.StartSymbol));
|
---|
| 46 | // select a target tree size uniformly in the possible range (as determined by explicit limits and limits of the grammar)
|
---|
| 47 | int treeSize = random.Next(allowedMinSize, allowedMaxSize);
|
---|
| 48 | SymbolicExpressionTree tree = new SymbolicExpressionTree();
|
---|
[1198] | 49 | do {
|
---|
[2730] | 50 | try {
|
---|
[3239] | 51 | tree.Root = PTC2(random, grammar, grammar.StartSymbol, treeSize + 1, maxTreeHeight + 1);
|
---|
[2730] | 52 | }
|
---|
| 53 | catch (ArgumentException) {
|
---|
| 54 | // try a different size
|
---|
[3223] | 55 | treeSize = random.Next(allowedMinSize, allowedMaxSize);
|
---|
[2730] | 56 | }
|
---|
[3223] | 57 | } while (tree.Root == null || tree.Size > maxTreeSize || tree.Height > maxTreeHeight);
|
---|
| 58 | return tree;
|
---|
| 59 | }
|
---|
| 60 |
|
---|
| 61 | private Symbol SelectRandomSymbol(IRandom random, IEnumerable<Symbol> symbols) {
|
---|
| 62 | var symbolList = symbols.ToList();
|
---|
| 63 | return symbolList[random.Next(symbolList.Count)];
|
---|
| 64 | }
|
---|
| 65 |
|
---|
| 66 |
|
---|
| 67 | private SymbolicExpressionTreeNode PTC2(IRandom random, ISymbolicExpressionGrammar grammar, Symbol rootSymbol, int size, int maxDepth) {
|
---|
| 68 | SymbolicExpressionTreeNode root = rootSymbol.CreateTreeNode();
|
---|
| 69 | if (size <= 1 || maxDepth <= 1) return root;
|
---|
| 70 | List<object[]> list = new List<object[]>();
|
---|
| 71 | int currentSize = 1;
|
---|
| 72 | int totalListMinSize = grammar.MinimalExpressionLength(rootSymbol) - 1;
|
---|
| 73 |
|
---|
| 74 | int actualArity = SampleArity(random, grammar, rootSymbol, size);
|
---|
| 75 | for (int i = 0; i < actualArity; i++) {
|
---|
| 76 | // insert a dummy sub-tree and add the pending extension to the list
|
---|
| 77 | root.AddSubTree(null);
|
---|
| 78 | list.Add(new object[] { root, i, 2 });
|
---|
| 79 | }
|
---|
| 80 |
|
---|
| 81 | // while there are pending extension points and we have not reached the limit of adding new extension points
|
---|
| 82 | while (list.Count > 0 && totalListMinSize + currentSize < size) {
|
---|
| 83 | int randomIndex = random.Next(list.Count);
|
---|
| 84 | object[] nextExtension = list[randomIndex];
|
---|
| 85 | list.RemoveAt(randomIndex);
|
---|
| 86 | SymbolicExpressionTreeNode parent = (SymbolicExpressionTreeNode)nextExtension[0];
|
---|
| 87 | int argumentIndex = (int)nextExtension[1];
|
---|
| 88 | int extensionDepth = (int)nextExtension[2];
|
---|
| 89 | if (extensionDepth + grammar.MinimalExpressionDepth(parent.Symbol) >= maxDepth) {
|
---|
| 90 | parent.RemoveSubTree(argumentIndex);
|
---|
| 91 | SymbolicExpressionTreeNode branch = CreateMinimalTree(random, grammar, grammar.AllowedSymbols(parent.Symbol, argumentIndex));
|
---|
| 92 | parent.InsertSubTree(argumentIndex, branch); // insert a smallest possible tree
|
---|
| 93 | currentSize += branch.GetSize();
|
---|
| 94 | totalListMinSize -= branch.GetSize();
|
---|
| 95 | } else {
|
---|
| 96 | var allowedSubFunctions = from s in grammar.AllowedSymbols(parent.Symbol, argumentIndex)
|
---|
| 97 | where grammar.MinimalExpressionDepth(parent.Symbol) + extensionDepth - 1 < maxDepth
|
---|
| 98 | where grammar.MaximalExpressionLength(s) > size - totalListMinSize - currentSize ||
|
---|
| 99 | totalListMinSize + currentSize >= size * 0.9 // if the necessary size is almost reached then also allow
|
---|
| 100 | // terminals or terminal-branches
|
---|
| 101 | select s;
|
---|
| 102 | Symbol selectedSymbol = SelectRandomSymbol(random, allowedSubFunctions);
|
---|
| 103 | SymbolicExpressionTreeNode newTree = selectedSymbol.CreateTreeNode();
|
---|
| 104 | parent.RemoveSubTree(argumentIndex);
|
---|
| 105 | parent.InsertSubTree(argumentIndex, newTree);
|
---|
| 106 | currentSize++;
|
---|
| 107 | totalListMinSize--;
|
---|
| 108 |
|
---|
| 109 | actualArity = SampleArity(random, grammar, selectedSymbol, size - currentSize);
|
---|
| 110 | for (int i = 0; i < actualArity; i++) {
|
---|
| 111 | // insert a dummy sub-tree and add the pending extension to the list
|
---|
| 112 | newTree.AddSubTree(null);
|
---|
| 113 | list.Add(new object[] { newTree, i, extensionDepth + 1 });
|
---|
| 114 | }
|
---|
| 115 | totalListMinSize += grammar.MinimalExpressionLength(selectedSymbol);
|
---|
| 116 | }
|
---|
| 117 | }
|
---|
| 118 | // fill all pending extension points
|
---|
| 119 | while (list.Count > 0) {
|
---|
| 120 | int randomIndex = random.Next(list.Count);
|
---|
| 121 | object[] nextExtension = list[randomIndex];
|
---|
| 122 | list.RemoveAt(randomIndex);
|
---|
| 123 | SymbolicExpressionTreeNode parent = (SymbolicExpressionTreeNode)nextExtension[0];
|
---|
| 124 | int a = (int)nextExtension[1];
|
---|
| 125 | int d = (int)nextExtension[2];
|
---|
| 126 | parent.RemoveSubTree(a);
|
---|
| 127 | parent.InsertSubTree(a,
|
---|
| 128 | CreateMinimalTree(random, grammar, grammar.AllowedSymbols(parent.Symbol, a))); // append a tree with minimal possible height
|
---|
| 129 | }
|
---|
[2447] | 130 | return root;
|
---|
[2210] | 131 | }
|
---|
[3223] | 132 |
|
---|
| 133 | private int SampleArity(IRandom random, ISymbolicExpressionGrammar grammar, Symbol symbol, int targetSize) {
|
---|
| 134 | // select actualArity randomly with the constraint that the sub-trees in the minimal arity can become large enough
|
---|
| 135 | int minArity = grammar.MinSubTrees(symbol);
|
---|
| 136 | int maxArity = grammar.MaxSubTrees(symbol);
|
---|
[3237] | 137 | if (maxArity > targetSize) {
|
---|
[3223] | 138 | maxArity = targetSize;
|
---|
| 139 | }
|
---|
| 140 | // the min number of sub-trees has to be set to a value that is large enough so that the largest possible tree is at least tree size
|
---|
| 141 | // if 1..3 trees are possible and the largest possible first sub-tree is smaller larger than the target size then minArity should be at least 2
|
---|
[3237] | 142 | long aggregatedLongestExpressionLength = 0;
|
---|
[3223] | 143 | for (int i = 0; i < maxArity; i++) {
|
---|
| 144 | aggregatedLongestExpressionLength += (from s in grammar.AllowedSymbols(symbol, i)
|
---|
[3237] | 145 | select grammar.MaximalExpressionLength(s)).Max();
|
---|
[3223] | 146 | if (aggregatedLongestExpressionLength < targetSize) minArity = i;
|
---|
| 147 | else break;
|
---|
| 148 | }
|
---|
| 149 |
|
---|
| 150 | // the max number of sub-trees has to be set to a value that is small enough so that the smallest possible tree is at most tree size
|
---|
| 151 | // if 1..3 trees are possible and the smallest possible first sub-tree is already larger than the target size then maxArity should be at most 0
|
---|
[3237] | 152 | long aggregatedShortestExpressionLength = 0;
|
---|
[3223] | 153 | for (int i = 0; i < maxArity; i++) {
|
---|
| 154 | aggregatedShortestExpressionLength += (from s in grammar.AllowedSymbols(symbol, i)
|
---|
[3237] | 155 | select grammar.MinimalExpressionLength(s)).Min();
|
---|
[3223] | 156 | if (aggregatedShortestExpressionLength > targetSize) {
|
---|
| 157 | maxArity = i;
|
---|
| 158 | break;
|
---|
| 159 | }
|
---|
| 160 | }
|
---|
| 161 | if (minArity > maxArity) throw new ArgumentException();
|
---|
| 162 | return random.Next(minArity, maxArity + 1);
|
---|
| 163 | }
|
---|
| 164 |
|
---|
| 165 | private SymbolicExpressionTreeNode CreateMinimalTree(IRandom random, ISymbolicExpressionGrammar grammar, IEnumerable<Symbol> symbols) {
|
---|
| 166 | // determine possible symbols that will lead to the smallest possible tree
|
---|
| 167 | var possibleSymbols = (from s in symbols
|
---|
| 168 | group s by grammar.MinimalExpressionLength(s) into g
|
---|
| 169 | orderby g.Key
|
---|
| 170 | select g).First();
|
---|
| 171 | var selectedSymbol = SelectRandomSymbol(random, possibleSymbols);
|
---|
| 172 | // build minimal tree by recursive application
|
---|
| 173 | var tree = selectedSymbol.CreateTreeNode();
|
---|
| 174 | for (int i = 0; i < grammar.MinSubTrees(selectedSymbol); i++)
|
---|
| 175 | tree.AddSubTree(CreateMinimalTree(random, grammar, grammar.AllowedSymbols(selectedSymbol, i)));
|
---|
| 176 | return tree;
|
---|
| 177 | }
|
---|
[2447] | 178 | }
|
---|
[645] | 179 | } |
---|