cs-tree-genetic-programming 1.0.1

#Overview

Tree-based genetic programming implemented using C#

Usage

Below shows the sample codes in which the symbolic regression is solved using TreeGP. The symbolic regression is trying to find a GP solution that approximate the function y = x^2 + x + 1.

class Program
{
	static double FunctionXY(double x)
	{
		return x * x + x + 1;
	}

	static DataTable LoadData()
	{
		DataTable table = new DataTable();
		table.Columns.Add("X");
		table.Columns.Add("Y");

		double lower_bound = -1.0;
		double upper_bound = 1.0;

		double interval = 0.1;

		for (double x = lower_bound; x <= upper_bound; x+=interval)
		{
			table.Rows.Add(x, FunctionXY(x));
		}


		return table;
	}
	static void Main(string[] args)
	{
		DataTable table = LoadData();

		TGPConfig config = new TGPConfig("TGPConfig.xml");

		// The problem is to minimize the sum of errors between predicted and actual function
		config.IsMaximization = false;

		// As specified in Chapter 4 of "A Field Guide to Genetic Programming"
		config.PopulationSize = 4;
		config.ElitismRatio = 0; //non elitist
		config.CrossoverRate = 0.5; // subtree crossover rate set to 0.5
		config.MacroMutationRate = 0.25; // subtree mutation rate set to 0.25; 
		config.MicroMutationRate = 0.0; // point mutation rate set to 0.0
		config.ReproductionRate = 0.25; // reproduction rate set to 0.25
		config.NormalizeEvolutionRates();
		//Question 1: Is the performance normal for the GP?

		config.MaximumDepthForCreation = 2;
		config.MaximumDepthForCrossover = 2; // no tree size limit by setting a very large max depth
		config.MaximumDepthForMutation = 2; 

		TGPPop<TGPSolution> pop = new TGPPop<TGPSolution>(config);
		pop.ReproductionSelectionInstruction = new SelectionInstruction_RouletteWheel<TGPSolution>(); //use roulette wheel selection 

		// Function Set = {+, -, %, *} where % is protected division that returns 1 if the denominator is 0
		pop.OperatorSet.AddOperator(new TGPOperator_Plus());
		pop.OperatorSet.AddOperator(new TGPOperator_Minus());
		pop.OperatorSet.AddOperator(new TGPOperator_Division());
		pop.OperatorSet.AddOperator(new TGPOperator_Multiplication());

		// Terminal Set = {R, x}
		pop.ConstantSet.AddConstant("R", DistributionModel.GetUniform()* 10.0 - 5.0);
		pop.VariableSet.AddVariable("x");

		pop.CreateFitnessCase += (index) =>
		{
			SymRegFitnessCase fitness_case = new SymRegFitnessCase();
			fitness_case.X = double.Parse(table.Rows[index]["X"].ToString());
			fitness_case.Y = double.Parse(table.Rows[index]["Y"].ToString());

			return fitness_case;
		};

		pop.GetFitnessCaseCount += () =>
		{
			return table.Rows.Count;
		};

		pop.EvaluateObjectiveForSolution += (fitness_cases, solution, objective_index) =>
		{
			double sum_of_error = 0;
			for (int i = 0; i < fitness_cases.Count; i++)
			{
				SymRegFitnessCase fitness_case = (SymRegFitnessCase)fitness_cases[i];
				double correct_y = fitness_case.Y;
				double computed_y = fitness_case.ComputedY;
				sum_of_error += System.Math.Abs(correct_y - computed_y);
			}

			return sum_of_error;
		};


		pop.BreedInitialPopulation();

		double error = pop.GlobalBestProgram.ObjectiveValue;
		while (error > 0.1)
		{
			pop.Evolve();
			error = pop.GlobalBestProgram.ObjectiveValue;

			Console.WriteLine("Symbolic Regression Generation: {0}", pop.CurrentGeneration);
			Console.WriteLine("Minimum Error: {0}", error.ToString("0.000"));
			Console.WriteLine("Global Best Solution:\n{0}", pop.GlobalBestProgram);
			
		}

		Console.WriteLine(pop.GlobalBestProgram.ToString());

	}
} 

The TGPConfig.xml can be found in the cs-tree-genetic-programming-samples/bin/Debug folder as well as the xml configuration for the various operators in the TreeGP (in the folder cs-tree-genetic-programming-samples/bin/Debug/symreg)