C# Application to Create and Recognize Mouse Gestures (.NET)

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml;

namespace NeuralNetworks.ActivationFunctions
{
	public class SigmoidFunction : IActivationFunction
	{
		private double m_Alpha;
		public double Alpha
		{
			get { return m_Alpha; }
			set 
			{
				if (value < 0)
					throw new ArgumentException("Alpha value must be strictly positive", "alpha");

				m_Alpha = value; 
			}
		}

		public SigmoidFunction()
			: this(1)
		{
		}

		public SigmoidFunction(double alpha)
		{
			if (alpha < 0)
				throw new ArgumentException("Alpha value must be strictly positive", "alpha");

			m_Alpha = alpha;
		}

		//Values are mapped in the interval [0,1]
		public double Compute(double value)
		{
			return (1 / (1 + Math.Exp(-m_Alpha * value)));
		}

		public double ComputeDerivateByOutput(double y)
		{
			return m_Alpha * y * (1 - y);
		}

		public double ComputeDerivateByInput(double x)
		{
			double output = Compute(x);
			return m_Alpha * output * (1 - output);
		}

		public override string ToString()
		{
			return "SigmoidFunction [" + m_Alpha.ToString() + "]";
		}

		public override bool Equals(object obj)
		{
			if (this == obj)
				return true;
			else
			{
				SigmoidFunction f = obj as SigmoidFunction;

				if (f == null)
					return false;
				else
				{
					if (m_Alpha != f.m_Alpha)
						return false;
					else
						return true;
				}
			}
		}

		public override int GetHashCode()
		{
			return base.GetHashCode() * m_Alpha.GetHashCode();
		}

		public void SerializeParameters(XmlWriter writer)
		{
			writer.WriteStartElement("parameters");
			writer.WriteAttributeString("alpha", m_Alpha.ToString());
			writer.WriteEndElement();
		}

		public void DeserializeParameters(XmlReader reader)
		{
			try
			{
				while (reader.Read())
				{
					switch (reader.NodeType)
					{
						case XmlNodeType.Element:
							{
								if (reader.Name == "parameters")
								{
									m_Alpha = double.Parse(reader["alpha"]);
									return;
								}
								break;
							}
					}
				}
			}
			catch (Exception exc)
			{
				Console.WriteLine("Exception caught while loading activation function data.\n\tSource: " + exc.Source + "\n\tMessage: " + exc.Message);
				m_Alpha = 1;
			}
		}
	}
}