#region License Information
/* HeuristicLab
* Copyright (C) 2002-2010 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.Collections.Generic;
using System.Linq;
using HeuristicLab.Core;
using HeuristicLab.Data;
using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding.Symbols;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding.Manipulators {
[StorableClass]
[Item("ChangeNodeTypeManipulation", "Selects a random tree node and changes the symbol size.")]
public class ChangeNodeTypeManipulation : SymbolicExpressionTreeManipulator {
public ChangeNodeTypeManipulation()
: base() {
}
protected override void Manipulate(IRandom random, SymbolicExpressionTree symbolicExpressionTree, ISymbolicExpressionGrammar grammar, IntValue maxTreeSize, IntValue maxTreeHeight, out bool success) {
// select any node except the with a parent where the parent is not the root node)
var manipulationPoint = (from parent in symbolicExpressionTree.Root.IterateNodesPrefix().Skip(1)
from subtree in parent.SubTrees
select new { Parent = parent, Node = subtree, Index = parent.SubTrees.IndexOf(subtree) }).SelectRandom(random);
// find possible symbols for the node (also considering the existing branches below it)
var allowedSymbols = from symbol in manipulationPoint.Parent.GetAllowedSymbols(manipulationPoint.Index)
where manipulationPoint.Node.SubTrees.Count <= manipulationPoint.Node.Grammar.GetMaxSubtreeCount(symbol)
where manipulationPoint.Node.SubTrees.Count >= manipulationPoint.Node.Grammar.GetMinSubtreeCount(symbol)
select symbol;
if (allowedSymbols.Count() <= 1) {
success = false;
return;
}
var node = manipulationPoint.Node;
// keep only symbols that are still possible considering the existing sub-trees
var constrainedSymbols = from symbol in allowedSymbols
let disallowedSubtrees =
from subtree in node.SubTrees
where !node.Grammar.IsAllowedChild(symbol, subtree.Symbol, node.SubTrees.IndexOf(subtree))
select subtree
where disallowedSubtrees.Count() == 0
select symbol;
if (constrainedSymbols.Count() <= 1) {
success = false;
return;
}
var newSymbol = SelectRandomSymbol(random, constrainedSymbols);
// replace the old node with the new node
var newNode = newSymbol.CreateTreeNode();
if (newNode.HasLocalParameters)
newNode.ResetLocalParameters(random);
foreach (var subtree in node.SubTrees)
newNode.AddSubTree(subtree);
manipulationPoint.Parent.RemoveSubTree(manipulationPoint.Index);
manipulationPoint.Parent.InsertSubTree(manipulationPoint.Index, newNode);
success = true;
}
private static Symbol SelectRandomSymbol(IRandom random, IEnumerable symbols) {
var symbolList = symbols.ToList();
var ticketsSum = symbolList.Select(x => x.InitialFrequency).Sum();
if (ticketsSum == 0.0) throw new ArgumentException("The initial frequency of all allowed symbols is zero.");
var r = random.NextDouble() * ticketsSum;
double aggregatedTickets = 0;
for (int i = 0; i < symbolList.Count; i++) {
aggregatedTickets += symbolList[i].InitialFrequency;
if (aggregatedTickets > r) {
return symbolList[i];
}
}
// this should never happen
throw new ArgumentException("There is a problem with the initial frequency setting of allowed symbols.");
}
}
}