Changeset 17665 for branches/2825-NSGA3/HeuristicLab.Algorithms.NSGA3/3.3/NSGA3.cs

Timestamp:

07/13/20 00:08:32 (4 years ago)

Author:

dleko

Message:

#2825 Refactoring: Move selection logic to its own static class.

File:

• branches/2825-NSGA3/HeuristicLab.Algorithms.NSGA3/3.3/NSGA3.cs (modified) (5 diffs)

branches/2825-NSGA3/HeuristicLab.Algorithms.NSGA3/3.3/NSGA3.cs

@@ -26 +26 @@
     public class NSGA3 : BasicAlgorithm
     {
-        private const double EPSILON = 10e-6; // a tiny number that is greater than 0
-
         public override bool SupportsPause => false;
 
@@ -53 +51 @@
 
         [Storable]
-        private List<Solution> solutions;
+        private List<Solution> solutions; // maybe todo: rename to nextGeneration (see Run method)
 
         #endregion Storable fields
@@ -266 +264 @@
                 // create copies of generated reference points (to preserve the original ones for
                 // the next generation) maybe todo: use cloner?
-                ToNextGeneration(CreateCopyOfReferencePoints());
+                //ToNextGeneration(CreateCopyOfReferencePoints());
+
+                List<Solution> qt = Mutate(Recombine(solutions));
+                List<Solution> rt = Utility.Concat(solutions, qt);
+
+                solutions = NSGA3Selection.SelectSolutionsForNextGeneration(rt, GetCopyOfReferencePoints(), Problem.Maximization, random);
+
                 ResultsCurrentGeneration.Value++;
             }
@@ -275 +279 @@
         #region Private Methods
 
-        private List<ReferencePoint> CreateCopyOfReferencePoints()
+        private List<ReferencePoint> GetCopyOfReferencePoints()
         {
             if (ReferencePoints == null) return null;
@@ -306 +310 @@
         {
             return Problem.Evaluate(new SingleEncodingIndividual(Problem.Encoding, new Scope { Variables = { new Variable(Problem.Encoding.Name, chromosome) } }), random);
-        }
-
-        private void ToNextGeneration(List<ReferencePoint> referencePoints)
-        {
-            List<Solution> st = new List<Solution>();
-            List<Solution> qt = Mutate(Recombine(solutions));
-            List<Solution> rt = Utility.Concat(solutions, qt);
-            List<Solution> nextGeneration;
-
-            // Do non-dominated sort
-            var qualities = Utility.ToFitnessMatrix(rt);
-            // compute the pareto fronts using the DominationCalculator and discard the qualities
-            // part in the inner tuples
-            Fronts = DominationCalculator<Solution>.CalculateAllParetoFronts(rt.ToArray(), qualities, Problem.Maximization, out int[] rank, true)
-                .Select(list => new List<Solution>(list.Select(pair => pair.Item1))).ToList();
-
-            int i = 0;
-            List<Solution> lf = null; // last front to be included
-            while (i < Fronts.Count && st.Count < PopulationSize.Value)
-            {
-                lf = Fronts[i];
-                st = Utility.Concat(st, lf);
-                i++;
-            }
-
-            if (st.Count == PopulationSize.Value) // no selection needs to be done
-                nextGeneration = st;
-            else
-            {
-                int l = i - 1;
-                nextGeneration = new List<Solution>();
-                for (int f = 0; f < l; f++)
-                    nextGeneration = Utility.Concat(nextGeneration, Fronts[f]);
-                int k = PopulationSize.Value - nextGeneration.Count;
-                Normalize(st);
-                Associate(referencePoints);
-                List<Solution> solutionsToAdd = Niching(k, referencePoints);
-                nextGeneration = Utility.Concat(nextGeneration, solutionsToAdd);
-            }
-        }
-
-        private void Normalize(List<Solution> population)
-        {
-            // Find the ideal point
-            double[] idealPoint = new double[NumberOfObjectives];
-            for (int j = 0; j < NumberOfObjectives; j++)
-            {
-                // Compute ideal point
-                idealPoint[j] = Utility.Min(s => s.Fitness[j], population);
-
-                // Translate objectives
-                foreach (var solution in population)
-                    solution.Fitness[j] -= idealPoint[j];
-            }
-
-            // Find the extreme points
-            Solution[] extremePoints = new Solution[NumberOfObjectives];
-            for (int j = 0; j < NumberOfObjectives; j++)
-            {
-                // Compute extreme points
-                double[] weights = new double[NumberOfObjectives];
-                for (int i = 0; i < NumberOfObjectives; i++) weights[i] = EPSILON;
-                weights[j] = 1;
-                double func(Solution s) => ASF(s.Fitness, weights);
-                extremePoints[j] = Utility.ArgMin(func, population);
-            }
-
-            // Compute intercepts
-            List<double> intercepts = GetIntercepts(extremePoints.ToList());
-
-            // Normalize objectives
-            NormalizeObjectives(intercepts, idealPoint);
-        }
-
-        private void NormalizeObjectives(List<double> intercepts, double[] idealPoint)
-        {
-            for (int f = 0; f < Fronts.Count; f++)
-            {
-                foreach (var solution in Fronts[f])
-                {
-                    for (int i = 0; i < NumberOfObjectives; i++)
-                    {
-                        if (Math.Abs(intercepts[i] - idealPoint[i]) > EPSILON)
-                        {
-                            solution.Fitness[i] = solution.Fitness[i] / (intercepts[i] - idealPoint[i]);
-                        }
-                        else
-                        {
-                            solution.Fitness[i] = solution.Fitness[i] / EPSILON;
-                        }
-                    }
-                }
-            }
-        }
-
-        private void Associate(List<ReferencePoint> referencePoints)
-        {
-            for (int f = 0; f < Fronts.Count; f++)
-            {
-                foreach (var solution in Fronts[f])
-                {
-                    // find reference point for which the perpendicular distance to the current
-                    // solution is the lowest
-                    var rpAndDist = Utility.MinArgMin(rp => GetPerpendicularDistance(rp.Values, solution.Fitness), referencePoints);
-                    // associated reference point
-                    var arp = rpAndDist.Item1;
-                    // distance to that reference point
-                    var dist = rpAndDist.Item2;
-
-                    if (f + 1 != Fronts.Count)
-                    {
-                        // Todo: Add member for reference point on index min_rp
-                        arp.NumberOfAssociatedSolutions++;
-                    }
-                    else
-                    {
-                        // Todo: Add potential member for reference point on index min_rp
-                        arp.AddPotentialAssociatedSolution(solution, dist);
-                    }
-                }
-            }
-        }
-
-        private List<Solution> Niching(int k, List<ReferencePoint> referencePoints)
-        {
-            List<Solution> solutions = new List<Solution>();
-            while (solutions.Count != k)
-            {
-                ReferencePoint min_rp = FindNicheReferencePoint(referencePoints);
-
-                Solution chosen = SelectClusterMember(min_rp);
-                if (chosen == null)
-                {
-                    referencePoints.Remove(min_rp);
-                }
-                else
-                {
-                    min_rp.NumberOfAssociatedSolutions++;
-                    min_rp.RemovePotentialAssociatedSolution(chosen);
-                    solutions.Add(chosen);
-                }
-            }
-
-            return solutions;
-        }
-
-        private ReferencePoint FindNicheReferencePoint(List<ReferencePoint> referencePoints)
-        {
-            // the minimum number of associated solutions for a reference point over all reference points
-            int minNumber = Utility.Min(rp => rp.NumberOfAssociatedSolutions, referencePoints);
-
-            // the reference points that share the number of associated solutions where that number
-            // is equal to minNumber
-            List<ReferencePoint> minAssociatedReferencePoints = new List<ReferencePoint>();
-            foreach (var referencePoint in referencePoints)
-                if (referencePoint.NumberOfAssociatedSolutions == minNumber)
-                    minAssociatedReferencePoints.Add(referencePoint);
-
-            if (minAssociatedReferencePoints.Count > 1)
-                return minAssociatedReferencePoints[random.Next(minAssociatedReferencePoints.Count)];
-            else
-                return minAssociatedReferencePoints.Single();
-        }
-
-        private Solution SelectClusterMember(ReferencePoint referencePoint)
-        {
-            Solution chosen = null;
-            if (referencePoint.HasPotentialMember())
-            {
-                if (referencePoint.NumberOfAssociatedSolutions == 0)
-                    chosen = referencePoint.FindClosestMember();
-                else
-                    chosen = referencePoint.RandomMember();
-            }
-            return chosen;
-        }
-
-        private double GetPerpendicularDistance(double[] values, double[] fitness)
-        {
-            double numerator = 0;
-            double denominator = 0;
-            for (int i = 0; i < values.Length; i++)
-            {
-                numerator += values[i] * fitness[i];
-                denominator += Math.Pow(values[i], 2);
-            }
-            double k = numerator / denominator;
-
-            double d = 0;
-            for (int i = 0; i < values.Length; i++)
-            {
-                d += Math.Pow(k * values[i] - fitness[i], 2);
-            }
-            return Math.Sqrt(d);
-        }
-
-        private double ASF(double[] x, double[] weight)
-        {
-            List<int> dimensions = new List<int>();
-            for (int i = 0; i < NumberOfObjectives; i++) dimensions.Add(i);
-            double f(int dim) => x[dim] / weight[dim];
-            return Utility.Max(f, dimensions);
-        }
-
-        private List<double> GetIntercepts(List<Solution> extremePoints)
-        {
-            // Check whether there are duplicate extreme points. This might happen but the original
-            // paper does not mention how to deal with it.
-            bool duplicate = false;
-            for (int i = 0; !duplicate && i < extremePoints.Count; i++)
-            {
-                for (int j = i + 1; !duplicate && j < extremePoints.Count; j++)
-                {
-                    // maybe todo: override Equals method of solution?
-                    duplicate = extremePoints[i].Equals(extremePoints[j]);
-                }
-            }
-
-            List<double> intercepts = new List<double>();
-
-            if (duplicate)
-            { // cannot construct the unique hyperplane (this is a casual method to deal with the condition)
-                for (int f = 0; f < NumberOfObjectives; f++)
-                {
-                    // extreme_points[f] stands for the individual with the largest value of
-                    // objective f
-                    intercepts.Add(extremePoints[f].Fitness[f]);
-                }
-            }
-            else
-            {
-                // Find the equation of the hyperplane
-                List<double> b = new List<double>(); //(pop[0].objs().size(), 1.0);
-                for (int i = 0; i < NumberOfObjectives; i++)
-                {
-                    b.Add(1.0);
-                }
-
-                List<List<double>> a = new List<List<double>>();
-                foreach (Solution s in extremePoints)
-                {
-                    List<double> aux = new List<double>();
-                    for (int i = 0; i < NumberOfObjectives; i++)
-                        aux.Add(s.Fitness[i]);
-                    a.Add(aux);
-                }
-                List<double> x = GaussianElimination(a, b);
-
-                // Find intercepts
-                for (int f = 0; f < NumberOfObjectives; f++)
-                {
-                    intercepts.Add(1.0 / x[f]);
-                }
-            }
-
-            return intercepts;
-        }
-
-        private List<double> GaussianElimination(List<List<double>> a, List<double> b)
-        {
-            List<double> x = new List<double>();
-
-            int n = a.Count;
-            for (int i = 0; i < n; i++)
-                a[i].Add(b[i]);
-
-            for (int @base = 0; @base < n - 1; @base++)
-                for (int target = @base + 1; target < n; target++)
-                {
-                    double ratio = a[target][@base] / a[@base][@base];
-                    for (int term = 0; term < a[@base].Count; term++)
-                        a[target][term] = a[target][term] - a[@base][term] * ratio;
-                }
-
-            for (int i = 0; i < n; i++)
-                x.Add(0.0);
-
-            for (int i = n - 1; i >= 0; i--)
-            {
-                for (int known = i + 1; known < n; known++)
-                    a[i][n] = a[i][n] - a[i][known] * x[known];
-                x[i] = a[i][n] / a[i][i];
-            }
-
-            return x;
         }