#region License Information
/* HeuristicLab
* Copyright (C) 2002-2014 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.Data;
using HeuristicLab.Parameters;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
using HeuristicLab.PluginInfrastructure;
namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
[NonDiscoverableType]
[StorableClass]
[Item("GrowTreeCreator", "An operator that creates new symbolic expression trees using the 'Grow' method")]
public class GrowTreeCreator : SymbolicExpressionTreeCreator,
ISymbolicExpressionTreeSizeConstraintOperator,
ISymbolicExpressionTreeGrammarBasedOperator {
private const string MaximumSymbolicExpressionTreeLengthParameterName = "MaximumSymbolicExpressionTreeLength";
private const string MaximumSymbolicExpressionTreeDepthParameterName = "MaximumSymbolicExpressionTreeDepth";
private const string SymbolicExpressionTreeGrammarParameterName = "SymbolicExpressionTreeGrammar";
private const string ClonedSymbolicExpressionTreeGrammarParameterName = "ClonedSymbolicExpressionTreeGrammar";
#region Parameter Properties
public IValueLookupParameter MaximumSymbolicExpressionTreeLengthParameter {
get { return (IValueLookupParameter)Parameters[MaximumSymbolicExpressionTreeLengthParameterName]; }
}
public IValueLookupParameter MaximumSymbolicExpressionTreeDepthParameter {
get { return (IValueLookupParameter)Parameters[MaximumSymbolicExpressionTreeDepthParameterName]; }
}
public IValueLookupParameter SymbolicExpressionTreeGrammarParameter {
get { return (IValueLookupParameter)Parameters[SymbolicExpressionTreeGrammarParameterName]; }
}
public ILookupParameter ClonedSymbolicExpressionTreeGrammarParameter {
get { return (ILookupParameter)Parameters[ClonedSymbolicExpressionTreeGrammarParameterName]; }
}
#endregion
#region Properties
public IntValue MaximumSymbolicExpressionTreeDepth {
get { return MaximumSymbolicExpressionTreeDepthParameter.ActualValue; }
}
public IntValue MaximumSymbolicExpressionTreeLength {
get { return MaximumSymbolicExpressionTreeLengthParameter.ActualValue; }
}
public ISymbolicExpressionGrammar ClonedSymbolicExpressionTreeGrammar {
get { return ClonedSymbolicExpressionTreeGrammarParameter.ActualValue; }
}
#endregion
[StorableConstructor]
protected GrowTreeCreator(bool deserializing) : base(deserializing) { }
protected GrowTreeCreator(GrowTreeCreator original, Cloner cloner) : base(original, cloner) { }
public GrowTreeCreator()
: base() {
Parameters.Add(new ValueLookupParameter(MaximumSymbolicExpressionTreeLengthParameterName,
"The maximal length (number of nodes) of the symbolic expression tree (this parameter is ignored)."));
Parameters.Add(new ValueLookupParameter(MaximumSymbolicExpressionTreeDepthParameterName,
"The maximal depth of the symbolic expression tree (a tree with one node has depth = 0)."));
Parameters.Add(new ValueLookupParameter(SymbolicExpressionTreeGrammarParameterName,
"The tree grammar that defines the correct syntax of symbolic expression trees that should be created."));
Parameters.Add(new LookupParameter(ClonedSymbolicExpressionTreeGrammarParameterName,
"An immutable clone of the concrete grammar that is actually used to create and manipulate trees."));
}
public override IDeepCloneable Clone(Cloner cloner) {
return new GrowTreeCreator(this, cloner);
}
public override IOperation InstrumentedApply() {
if (ClonedSymbolicExpressionTreeGrammarParameter.ActualValue == null) {
SymbolicExpressionTreeGrammarParameter.ActualValue.ReadOnly = true;
IScope globalScope = ExecutionContext.Scope;
while (globalScope.Parent != null)
globalScope = globalScope.Parent;
globalScope.Variables.Add(new Variable(ClonedSymbolicExpressionTreeGrammarParameterName,
(ISymbolicExpressionGrammar)SymbolicExpressionTreeGrammarParameter.ActualValue.Clone()));
}
return base.InstrumentedApply();
}
protected override ISymbolicExpressionTree Create(IRandom random) {
return Create(random, ClonedSymbolicExpressionTreeGrammar,
MaximumSymbolicExpressionTreeLength.Value, MaximumSymbolicExpressionTreeDepth.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();
rootNode.SetGrammar(new SymbolicExpressionTreeGrammar(grammar));
if (rootNode.HasLocalParameters) rootNode.ResetLocalParameters(random);
var startNode = (SymbolicExpressionTreeTopLevelNode)grammar.StartSymbol.CreateTreeNode();
if (startNode.HasLocalParameters) startNode.ResetLocalParameters(random);
startNode.SetGrammar(new SymbolicExpressionTreeGrammar(grammar));
rootNode.AddSubtree(startNode);
Create(random, startNode, maxTreeDepth - 2);
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();
var selectedSymbol = possibleSymbols.SelectRandom(weights, random);
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)
throw new ArgumentException("Cannot grow node of arity zero. Expected a function node.");
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();
var selectedSymbol = possibleSymbols.SelectRandom(weights, random);
var tree = selectedSymbol.CreateTreeNode();
if (tree.HasLocalParameters) tree.ResetLocalParameters(random);
root.AddSubtree(tree);
}
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);
}
}
}