Some fixes

Author: ZviRosenfeldCx

GeneticAlgorithm.UnitTests/PopulationRenwalManagerTests.cs

@@ -24,6 +24,21 @@ public void RenewAtConvergenceTest()
             Assert.AreEqual(4, result.BestChromosome.Evaluate());
         }
 
+        [TestMethod]
+        public void RenewOnlySomeChromosomes()
+        {
+            var populationManager = new TestPopulationManager(new double[] { 4, 4, 4 }, false);
+            populationManager.SetPopulationGenerated(new[]
+                {new double[] {3, 3, 3}, new double[] {2, 2, 2}, new double[] {1, 1, 1}});
+            var engine = new TestGeneticSearchEngineBuilder(POPULATION_SIZE, MAX_GENERATIONS, populationManager)
+                .AddPopulationRenwalManager(new RenewAtConvergence(0.9, 0.5))
+                .IncludeAllHistory().Build();
+
+            var result = engine.Search();
+
+            Assert.AreEqual(4, result.BestChromosome.Evaluate());
+        }
+
         [TestMethod]
         public void RenewIfNoImprovmentTest1()
         {

GeneticAlgorithm/Exceptions/InternalSearchException.cs

@@ -0,0 +1,9 @@
+namespace GeneticAlgorithm.Exceptions
+{
+    class InternalSearchException : GeneticAlgorithmException
+    {
+        public InternalSearchException(string message) : base(message)
+        {
+        }
+    }
+}

GeneticAlgorithm/GeneticSearchEngine.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
@@ -80,8 +79,34 @@ private int GetPopulationToRenew(int generation)
         private void RenewPopulation(int populationToRenew)
         {
             var newPopulation = populationGenerator.GeneratePopulation(populationToRenew).ToArray();
-            for (int i = 0; i < populationToRenew; i++)
+            var oldPopulation = GetBestChromosomes(population.Length - populationToRenew);
+            var i = 0;
+            for (; i < populationToRenew; i++)
                 population[i] = newPopulation[i];
+            for (; i < population.Length; i++)
+                population[i] = oldPopulation[i - populationToRenew];
+        }
+
+        private IChromosome[] GetBestChromosomes(int n)
+        {
+            if (n == 0)
+                return new IChromosome[0];
+
+            var min = evaluations.OrderByDescending(x => x).Take(n).Last();
+            var bestChromosomes = new IChromosome[n];
+            int index = 0;
+            for (int i = 0; i < population.Length; i++)
+            {
+                if (evaluations[i] >= min)
+                {
+                    bestChromosomes[index] = population[i];
+                    index++;
+                }
+                if (index >= n)
+                    return bestChromosomes;
+            }
+
+            throw new InternalSearchException("Code 1000 (not enough best chromosomes found)");
         }
 
         private void EvaluatePopulation()

GeneticAlgorithm/GeneticSearchEngineBuilder.cs

@@ -29,6 +29,9 @@ public GeneticSearchEngineBuilder SetMutationProbability(double probability)
             return this;
         }
 
+        /// <summary>
+        /// The GeneticSearchResult will include the entire history of the population
+        /// </summary>
         public GeneticSearchEngineBuilder IncludeAllHistory()
         {
             includeAllHistory = true;

GeneticAlgorithm/GeneticSearchOptions.cs

@@ -31,10 +31,7 @@ public GeneticSearchOptions(int populationSize, int maxGenerations, double mutat
         public int MaxGenerations { get; }
 
         public double MutationProbability { get; }
-
-        /// <summary>
-        /// If this is true, the GeneticSearchResult will include the entire history of the population
-        /// </summary>
+        
         public bool IncludeAllHistory { get; }
 
         public List<IStopManager> StopManagers { get; }

GeneticAlgorithm/Interfaces/IPopulationGenerator.cs

@@ -4,6 +4,9 @@ namespace GeneticAlgorithm.Interfaces
 {
     public interface IPopulationGenerator
     {
+        /// <summary>
+        /// size is the number of chromosomes we want to generate
+        /// </summary>
         IEnumerable<IChromosome> GeneratePopulation(int size);
     }
 }

README.md

@@ -33,7 +33,8 @@ You'll need to implement the ICrossoverManager class. This tells the engine how
 
 ### IPopulationGenerator
 
-You'll also need to implement the IPopulationGenerator class. The engine uses this class to create its initial population. the PopulationGeneratorwill also renew the population when needed (see the secssion on IPopulationRenwalManagers).
+You'll also need to implement the IPopulationGenerator class. The engine uses this class to create its initial population. 
+The PopulationGenerator will also renew the population when needed (see [IPopulationRenwalManagers](https://github.com/ZviRosenfeld/GeneticAlgorithmEngine/blob/master/README.md#ipopulationrenwalmanagers)).
 
 ```CSharp
     public interface IPopulationGenerator
@@ -58,6 +59,8 @@ var result = searchEngine.Search();
 
 ## Search Options
 
+Let's see how we can configure our search engine to better match our needs.
+
 ### Mutations
 
 By defualt, the probability of mutations is 0. You can change this be using the GeneticSearchEngineBuilder.SetMutationProbability(double probability) method.