#region License Information
/* HeuristicLab
* Copyright (C) 2002-2015 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
*
* This file is part of HeuristicLab.
*
* HeuristicLab is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* HeuristicLab is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with HeuristicLab. If not, see .
*/
#endregion
using System;
using System.Linq;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
using HeuristicLab.PluginInfrastructure;
namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
[NonDiscoverableType]
[StorableType("F117AE18-7FFC-4AD7-9493-FB0E54E17D19")]
[Item("GrowTreeCreator", "An operator that creates new symbolic expression trees using the 'Grow' method")]
public class GrowTreeCreator : SymbolicExpressionTreeCreator {
[StorableConstructor]
protected GrowTreeCreator(bool deserializing) : base(deserializing) { }
protected GrowTreeCreator(GrowTreeCreator original, Cloner cloner) : base(original, cloner) { }
public GrowTreeCreator() : base() { }
public override IDeepCloneable Clone(Cloner cloner) {
return new GrowTreeCreator(this, cloner);
}
protected override ISymbolicExpressionTree Create(IRandom random) {
return Create(random, ClonedSymbolicExpressionTreeGrammarParameter.ActualValue,
MaximumSymbolicExpressionTreeLengthParameter.ActualValue.Value, MaximumSymbolicExpressionTreeDepthParameter.ActualValue.Value);
}
public override ISymbolicExpressionTree CreateTree(IRandom random, ISymbolicExpressionGrammar grammar, int maxTreeLength, int maxTreeDepth) {
return Create(random, grammar, maxTreeLength, maxTreeDepth);
}
///
/// Create a symbolic expression tree using the 'Grow' method.
/// All symbols are allowed for nodes, so the resulting trees can be of any shape and size.
///
/// Random generator
/// Available tree grammar
/// Maximum tree depth
/// Maximum tree length. This parameter is not used.
///
public static ISymbolicExpressionTree Create(IRandom random, ISymbolicExpressionGrammar grammar, int maxTreeLength, int maxTreeDepth) {
var tree = new SymbolicExpressionTree();
var rootNode = (SymbolicExpressionTreeTopLevelNode)grammar.ProgramRootSymbol.CreateTreeNode();
if (rootNode.HasLocalParameters) rootNode.ResetLocalParameters(random);
rootNode.SetGrammar(grammar.CreateExpressionTreeGrammar());
var startNode = (SymbolicExpressionTreeTopLevelNode)grammar.StartSymbol.CreateTreeNode();
if (startNode.HasLocalParameters) startNode.ResetLocalParameters(random);
startNode.SetGrammar(grammar.CreateExpressionTreeGrammar());
rootNode.AddSubtree(startNode);
Create(random, startNode, maxTreeDepth - 1);
tree.Root = rootNode;
return tree;
}
public static void Create(IRandom random, ISymbolicExpressionTreeNode seedNode, int maxDepth) {
// make sure it is possible to create a trees smaller than maxDepth
if (seedNode.Grammar.GetMinimumExpressionDepth(seedNode.Symbol) > maxDepth)
throw new ArgumentException("Cannot create trees of depth " + maxDepth + " or smaller because of grammar constraints.", "maxDepth");
var arity = SampleArity(random, seedNode);
// throw an exception if the seedNode happens to be a terminal, since in this case we cannot grow a tree
if (arity <= 0)
throw new ArgumentException("Cannot grow tree. Seed node shouldn't have arity zero.");
var allowedSymbols = seedNode.Grammar.AllowedSymbols.Where(s => s.InitialFrequency > 0.0).ToList();
for (var i = 0; i < arity; i++) {
var possibleSymbols = allowedSymbols.Where(s => seedNode.Grammar.IsAllowedChildSymbol(seedNode.Symbol, s, i)).ToList();
var weights = possibleSymbols.Select(s => s.InitialFrequency).ToList();
#pragma warning disable 612, 618
var selectedSymbol = possibleSymbols.SelectRandom(weights, random);
#pragma warning restore 612, 618
var tree = selectedSymbol.CreateTreeNode();
if (tree.HasLocalParameters) tree.ResetLocalParameters(random);
seedNode.AddSubtree(tree);
}
// Only iterate over the non-terminal nodes (those which have arity > 0)
// Start from depth 2 since the first two levels are formed by the rootNode and the seedNode
foreach (var subTree in seedNode.Subtrees)
if (subTree.Grammar.GetMaximumSubtreeCount(subTree.Symbol) > 0)
RecursiveCreate(random, subTree, 2, maxDepth);
}
private static void RecursiveCreate(IRandom random, ISymbolicExpressionTreeNode root, int currentDepth, int maxDepth) {
var arity = SampleArity(random, root);
if (arity == 0)
return;
var allowedSymbols = root.Grammar.AllowedSymbols.Where(s => s.InitialFrequency > 0.0).ToList();
for (var i = 0; i < arity; i++) {
var possibleSymbols = allowedSymbols.Where(s => root.Grammar.IsAllowedChildSymbol(root.Symbol, s, i) &&
root.Grammar.GetMinimumExpressionDepth(s) - 1 <= maxDepth - currentDepth).ToList();
if (!possibleSymbols.Any())
throw new InvalidOperationException("No symbols are available for the tree.");
var weights = possibleSymbols.Select(s => s.InitialFrequency).ToList();
#pragma warning disable 612, 618
var selectedSymbol = possibleSymbols.SelectRandom(weights, random);
#pragma warning restore 612, 618
var tree = selectedSymbol.CreateTreeNode();
if (tree.HasLocalParameters) tree.ResetLocalParameters(random);
root.AddSubtree(tree);
}
if (maxDepth > currentDepth)
foreach (var subTree in root.Subtrees)
if (subTree.Grammar.GetMaximumSubtreeCount(subTree.Symbol) != 0)
RecursiveCreate(random, subTree, currentDepth + 1, maxDepth);
}
private static int SampleArity(IRandom random, ISymbolicExpressionTreeNode node) {
var minArity = node.Grammar.GetMinimumSubtreeCount(node.Symbol);
var maxArity = node.Grammar.GetMaximumSubtreeCount(node.Symbol);
return random.Next(minArity, maxArity + 1);
}
}
}