FitnessStagnationTermination.cs

using System.ComponentModel;

namespace GeneticSharp
{
    /// <summary>
    /// Fitness Stagnation Termination.    
    /// <remarks>
    /// The genetic algorithm will be terminate when the best chromosome's fitness has no change in the last generations specified.
    /// </remarks>
    /// </summary>
    [DisplayName("Fitness Stagnation")]
    public class FitnessStagnationTermination : TerminationBase
    {
        #region Fields
        private double m_lastFitness;
        private int m_stagnantGenerationsCount;
        #endregion

        #region Constructors
        /// <summary>
        /// Initializes a new instance of the <see cref="FitnessStagnationTermination"/> class.
        /// </summary>
        /// <remarks>
        /// The ExpectedStagnantGenerationsNumber default value is 100.
        /// </remarks>
        public FitnessStagnationTermination() : this(100)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="FitnessStagnationTermination"/> class.
        /// </summary>
        /// <param name="expectedStagnantGenerationsNumber">The expected stagnant generations number to reach the termination.</param>
        public FitnessStagnationTermination(int expectedStagnantGenerationsNumber)
        {
            ExpectedStagnantGenerationsNumber = expectedStagnantGenerationsNumber;
        }
        #endregion

        #region Properties
        /// <summary>
        /// Gets or sets the expected stagnant generations number to reach the termination.
        /// </summary>
        public int ExpectedStagnantGenerationsNumber { get; set; }
        #endregion

        #region Methods
        /// <summary>
        /// Determines whether the specified geneticAlgorithm reached the termination condition.
        /// </summary>
        /// <returns>True if termination has been reached, otherwise false.</returns>
        /// <param name="geneticAlgorithm">The genetic algorithm.</param>
        protected override bool PerformHasReached(IGeneticAlgorithm geneticAlgorithm)
        {
            var bestFitness = geneticAlgorithm.BestChromosome.Fitness.Value;

            if (m_lastFitness == bestFitness)
            {
                m_stagnantGenerationsCount++;
            }
            else
            {
                m_stagnantGenerationsCount = 1;
            }

            m_lastFitness = bestFitness;

            return m_stagnantGenerationsCount >= ExpectedStagnantGenerationsNumber;
        }
        #endregion
    }
}