public Population <Expression <Func <double, double> > > GeneratePopulation()
{
this.CheckForDispose();
var chromosomes = new List <Chromosome <Expression <Func <double, double> > > >();
while (chromosomes.Count < ExpressionEvolverGeneticAlgorithmParameters.PopulationSizeValue)
{
var parameter = Expression.Parameter(typeof(double), "a");
var maximumExpressions = this.Random.Next(
ExpressionEvolverGeneticAlgorithmParameters.ExpressionMaximum);
var body = new RandomExpressionGenerator(maximumExpressions,
ExpressionEvolverGeneticAlgorithmParameters.InjectConstantProbabilityValue,
ExpressionEvolverGeneticAlgorithmParameters.ConstantLimit,
parameter, this.Random).Body.Compress();
if (body.IsValid())
{
var value = Expression.Lambda <Func <double, double> >(body, parameter);
chromosomes.Add(new Chromosome <Expression <Func <double, double> > >(
value, this.FitnessEvaluator(value)));
}
}
return(new Population <Expression <Func <double, double> > >(chromosomes));
}
private void GetRandomOperation(Operators @operator)
{
var isLeftConstant = this.Random.NextDouble() < this.InjectConstantProbabilityValue;
var isRightConstant = this.Random.NextDouble() < this.InjectConstantProbabilityValue;
var isLeftBody = true;
var isRightBody = true;
if (!isLeftConstant && !isRightConstant)
{
isLeftBody = this.Random.NextDouble() < 0.5;
isRightBody = !isLeftBody;
}
else if (isLeftConstant && isRightConstant)
{
isLeftConstant = this.Random.NextDouble() < this.InjectConstantProbabilityValue;
isRightConstant = !isLeftConstant;
}
else if (@operator == Operators.Divide && !isLeftConstant && !isRightConstant)
{
isLeftConstant = this.Random.NextBoolean();
isRightConstant = !isLeftConstant;
}
this.Body = RandomExpressionGenerator.GetExpressionFunction(@operator)(
isLeftConstant ? this.GetConstant() : (isLeftBody ? this.Body : this.Parameter),
isRightConstant ? this.GetConstant() : (isRightBody ? this.Body : this.Parameter));
}
public Expression <Func <double, double> > Mutator(Expression <Func <double, double> > chromosome)
{
this.CheckForDispose();
chromosome.CheckParameterForNull("chromosome");
Expression <Func <double, double> > mutated = null;
if (this.Random.NextDouble() < this.MutationProbability)
{
var chromosomeBody = chromosome.Body;
var nodeCount = chromosomeBody.GetNodeCount();
var selectedNodeIndex = this.Random.Next(nodeCount);
var selectedNode = chromosomeBody.GetNode(selectedNodeIndex);
var selectedNodeCount = selectedNode.GetNodeCount();
var mutatedNode = new RandomExpressionGenerator(this.Random.Next(selectedNodeCount),
ExpressionEvolverGeneticAlgorithmParameters.InjectConstantProbabilityValue,
ExpressionEvolverGeneticAlgorithmParameters.ConstantLimit,
chromosome.Parameters[0], this.Random).Body;
chromosomeBody = chromosomeBody.Replace(null, selectedNode, mutatedNode).Compress();
mutated = Expression.Lambda <Func <double, double> >(chromosomeBody,
(from param in chromosome.Parameters
select param));
}
else
{
mutated = chromosome;
}
return(mutated.IsValid() ? mutated : null);
}