Fix #72 - GeneticAlgorithm.BestChromosome.Fitness decrease over time …

…when using EliteSelection

src/GeneticSharp.Domain.UnitTests/Populations/PopulationTest.cs

@@ -82,6 +82,38 @@ public void EndCurrentGeneration_BestChromosomeChanged_ChangeEventRaise()
 
             Assert.IsTrue(eventRaise);
         }
+
+        /// <summary>
+        /// https://github.com/giacomelli/GeneticSharp/issues/70
+        /// </summary>
+        [Test]
+        public void EndCurrentGeneration_Issue70_Solved()
+        {
+            var target = new Population(100, 100, new ChromosomeStub());
+
+            var eventRaise = false;
+            IChromosome lastChromosome = null;
+
+            target.BestChromosomeChanged += (e, a) =>
+            {
+                eventRaise = true;
+
+                if (lastChromosome != null && lastChromosome.Fitness == target.BestChromosome.Fitness)
+                    Assert.Fail("BestChromosomeChanged should only be raised if fitness is different.");
+
+                lastChromosome = target.BestChromosome;
+            };
+
+            target.CreateInitialGeneration();
+            target.CurrentGeneration.Chromosomes.Each(c => c.Fitness = 0);
+            target.CurrentGeneration.Chromosomes[1].Fitness = 1;
+            target.EndCurrentGeneration();
+
+            target.CurrentGeneration.Chromosomes[0].Fitness = 1;            
+            target.EndCurrentGeneration();
+
+            Assert.IsTrue(eventRaise);
+        }
     }
 }
 

src/GeneticSharp.Domain.UnitTests/Selections/EliteSelectionTest.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using NUnit.Framework;
 using NSubstitute;
+using System.Linq;
 
 namespace GeneticSharp.Domain.UnitTests.Selections
 {
@@ -72,8 +73,46 @@ public void SelectChromosomes_Generation_ChromosomesSelected()
             actual = target.SelectChromosomes(3, generation);
             Assert.AreEqual(3, actual.Count);
             Assert.AreEqual(0.7, actual[0].Fitness);
-            Assert.AreEqual(0.5, actual[1].Fitness);
-            Assert.AreEqual(0.1, actual[2].Fitness);
+            Assert.AreEqual(0.7, actual[1].Fitness);
+            Assert.AreEqual(0.5, actual[2].Fitness);
+        }
+
+        /// <summary>
+        /// https://github.com/giacomelli/GeneticSharp/issues/72
+        /// </summary>
+        [Test()]
+        public void SelectChromosomes_Issue72_Solved()
+        {
+            var target = new EliteSelection();
+            var chromosomes = new IChromosome[10];
+
+            for (int i = 0; i < chromosomes.Length; i++)
+            {                
+                var c = Substitute.ForPartsOf<ChromosomeBase>(2);
+                c.Fitness = i;
+                chromosomes[i] = c;
+            }
+
+            var generation3 = new Generation(3, chromosomes.Take(4).ToList());            
+            var generation2 = new Generation(2, chromosomes.Skip(4).Take(3).ToList());
+            var generation1 = new Generation(1, chromosomes.Skip(7).Take(3).ToList());
+
+
+            var actual = target.SelectChromosomes(2, generation1);
+            Assert.AreEqual(2, actual.Count);
+            Assert.AreEqual(9, actual[0].Fitness);
+            Assert.AreEqual(8, actual[1].Fitness);
+
+            actual = target.SelectChromosomes(3, generation2);
+            Assert.AreEqual(3, actual.Count);
+            Assert.AreEqual(9, actual[0].Fitness);
+            Assert.AreEqual(6, actual[1].Fitness);
+            Assert.AreEqual(5, actual[2].Fitness);            
+
+            actual = target.SelectChromosomes(2, generation3);
+            Assert.AreEqual(2, actual.Count);
+            Assert.AreEqual(9, actual[0].Fitness);
+            Assert.AreEqual(3, actual[1].Fitness);
         }
     }
 }

src/GeneticSharp.Domain.UnitTests/Selections/SelectionServiceTest.cs

@@ -12,26 +12,27 @@ public void GetSelectionTypes_NoArgs_AllAvailableSelections()
         {
             var actual = SelectionService.GetSelectionTypes();
 
-            Assert.AreEqual(5, actual.Count);
+            Assert.AreEqual(6, actual.Count);
             Assert.AreEqual(typeof(EliteSelection), actual[0]);
             Assert.AreEqual(typeof(RankSelection), actual[1]);
             Assert.AreEqual(typeof(RouletteWheelSelection), actual[2]);
             Assert.AreEqual(typeof(StochasticUniversalSamplingSelection), actual[3]);
             Assert.AreEqual(typeof(TournamentSelection), actual[4]);
-
+            Assert.AreEqual(typeof(TruncationSelection), actual[5]);
         }
 
         [Test()]
         public void GetSelectionNames_NoArgs_AllAvailableSelectionsNames()
         {
             var actual = SelectionService.GetSelectionNames();
 
-            Assert.AreEqual(5, actual.Count);
+            Assert.AreEqual(6, actual.Count);
             Assert.AreEqual("Elite", actual[0]);
             Assert.AreEqual("Rank", actual[1]);
             Assert.AreEqual("Roulette Wheel", actual[2]);
             Assert.AreEqual("Stochastic Universal Sampling", actual[3]);
             Assert.AreEqual("Tournament", actual[4]);
+            Assert.AreEqual("Truncation", actual[5]);
         }
 
         [Test()]
@@ -48,7 +49,7 @@ public void CreateSelectionByName_ValidNameButInvalidConstructorArgs_Exception()
         {
             Assert.Catch<ArgumentException>(() =>
             {
-                SelectionService.CreateSelectionByName("Elite", 1);
+                SelectionService.CreateSelectionByName("Elite", 1, 2);
             }, "A ISelection's implementation with name 'Elite' was found, but seems the constructor args were invalid.");
         }
 

src/GeneticSharp.Domain/Populations/Population.cs

@@ -8,7 +8,11 @@ namespace GeneticSharp
     /// </summary>
     public class Population : IPopulation
     {
-        #region Constructors
+        /// <summary>
+        /// Occurs when best chromosome changed.
+        /// </summary>
+        public event EventHandler BestChromosomeChanged;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="GeneticSharp.Domain.Populations.Population"/> class.
         /// </summary>
@@ -36,16 +40,7 @@ public Population(int minSize, int maxSize, IChromosome adamChromosome)
             Generations = new List<Generation>();
             GenerationStrategy = new PerformanceGenerationStrategy(10);
         }
-        #endregion
-
-        #region Events
-        /// <summary>
-        /// Occurs when best chromosome changed.
-        /// </summary>
-        public event EventHandler BestChromosomeChanged;
-        #endregion
-
-        #region Properties
+
         /// <summary>
         /// Gets or sets the creation date.
         /// </summary>
@@ -101,10 +96,8 @@ public Population(int minSize, int maxSize, IChromosome adamChromosome)
         /// Gets or sets the original chromosome of all population.
         /// </summary>
         /// <value>The adam chromosome.</value>
-        protected IChromosome AdamChromosome { get; set; }
-        #endregion
-
-        #region Public methods
+        protected IChromosome AdamChromosome { get; set; }        
+
         /// <summary>
         /// Creates the initial generation.
         /// </summary>
@@ -159,18 +152,15 @@ public virtual void EndCurrentGeneration()
 
                 OnBestChromosomeChanged(EventArgs.Empty);
             }
-        }
-        #endregion
-
-        #region Protected methods
+        }        
+
         /// <summary>
         /// Raises the best chromosome changed event.
         /// </summary>
         /// <param name="args">The event arguments.</param>
         protected virtual void OnBestChromosomeChanged(EventArgs args)
         {
             BestChromosomeChanged?.Invoke(this, args);
-        }
-        #endregion
+        }        
     }
 }

src/GeneticSharp.Domain/Selections/EliteSelection.cs

@@ -5,22 +5,35 @@
 namespace GeneticSharp
 {
     /// <summary>
-    /// Selects the chromosomes with the best fitness.
+    /// Selects the chromosomes with the best fitness and a small portion of the best individuals
+    /// from the last generation is carried over (without any changes) to the next one.
     /// </summary>
     /// <remarks>
-    /// Also know as: Truncation Selection.
-    /// </remarks>    
+    /// <see href="https://en.wikipedia.org/wiki/Selection_(genetic_algorithm)">Wikipedia</see>
+    /// </remarks>
     [DisplayName("Elite")]
     public sealed class EliteSelection : SelectionBase
     {
-        #region Constructors
+        int _previousGenerationChromosomesNumber;
+        List<IChromosome> _previousGenerationChromosomes = new List<IChromosome>();
+
         /// <summary>
         /// Initializes a new instance of the <see cref="GeneticSharp.Domain.Selections.EliteSelection"/> class.
         /// </summary>
-        public EliteSelection() : base(2)
+        public EliteSelection() 
+            : this(1)
         {
         }
-        #endregion
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="GeneticSharp.Domain.Selections.EliteSelection"/> class.
+        /// </summary>
+        /// <param name="previousGenerationChromosomesNumber">The number of best chromosomes of the previous generation to carried over to the next one.</param>
+        public EliteSelection(int previousGenerationChromosomesNumber) 
+            : base(2)
+        {
+            _previousGenerationChromosomesNumber = previousGenerationChromosomesNumber;
+        }
 
         #region ISelection implementation
         /// <summary>
@@ -31,8 +44,14 @@ public EliteSelection() : base(2)
         /// <returns>The select chromosomes.</returns>
         protected override IList<IChromosome> PerformSelectChromosomes(int number, Generation generation)
         {
-            var ordered = generation.Chromosomes.OrderByDescending(c => c.Fitness);
-            return ordered.Take(number).ToList();
+            _previousGenerationChromosomes.AddRange(generation.Chromosomes);
+
+            var ordered = _previousGenerationChromosomes.OrderByDescending(c => c.Fitness);
+            var result = ordered.Take(number).ToList();
+
+            _previousGenerationChromosomes = result.Take(_previousGenerationChromosomesNumber).ToList();
+
+            return result;
         }
 
         #endregion

src/GeneticSharp.Domain/Selections/SelectionBase.cs

@@ -9,11 +9,8 @@ namespace GeneticSharp
     /// </summary>
     public abstract class SelectionBase : ISelection
     {
-        #region Fields
-        private readonly int m_minNumberChromosomes;
-        #endregion
+        readonly int m_minNumberChromosomes;
 
-        #region Constructors
         /// <summary>
         /// Initializes a new instance of the <see cref="GeneticSharp.Domain.Selections.SelectionBase"/> class.
         /// </summary>
@@ -22,9 +19,7 @@ protected SelectionBase(int minNumberChromosomes)
         {
             m_minNumberChromosomes = minNumberChromosomes;
         }
-        #endregion
-
-        #region ISelection implementation
+
         /// <summary>
         /// Selects the number of chromosomes from the generation specified.
         /// </summary>
@@ -56,7 +51,6 @@ public IList<IChromosome> SelectChromosomes(int number, Generation generation)
         /// <returns>The selected chromosomes.</returns>
         /// <param name="number">The number of chromosomes to select.</param>
         /// <param name="generation">The generation where the selection will be made.</param>
-        protected abstract IList<IChromosome> PerformSelectChromosomes(int number, Generation generation);
-        #endregion
+        protected abstract IList<IChromosome> PerformSelectChromosomes(int number, Generation generation);        
     }
 }

src/GeneticSharp.Extensions.UnitTests/Multiple/MultipleTest.cs

@@ -15,7 +15,7 @@ class MultipleTest
         public void Evolve_CompareToSingleChromosome_Evolved()
         {
             int numberOfCities = 30;
-            var selection = new EliteSelection();
+            var selection = new TruncationSelection();
             var crossover = new UniformCrossover();
             var mutation = new TworsMutation();