source: branches/HeuristicLab.Problems.MultiObjectiveTestFunctions/HeuristicLab.Problems.MultiObjectiveTestFunctions/3.3/Calculators/Crowding.cs @ 13936

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2016 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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 * This file is part of HeuristicLab.
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 * HeuristicLab is free software: you can redistribute it and/or modify
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 * GNU General Public License for more details.
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#endregion

using System;
using System.Collections.Generic;
using System.Linq;

namespace HeuristicLab.Problems.MultiObjectiveTestFunctions
{

    /// <summary>
    /// Crowding distance d(x,A) is usually defined between a point x and a set of points A
    /// d(x,A) is then a weighted sum over all dimensions where for each dimension the next larger and the next smaller Point to x are subtracted
    /// I extended the concept and defined the Crowding distance of a front A as the mean of the crowding distances of every point x in A 
    /// C(A) = mean(d(x,A)) where x in A  and d(x,A) is not infinite 
    /// </summary>
    public class Crowding
    {

        public static double Calculate(IEnumerable<double[]> front, double[,] bounds)
        {
            double sum = 0;
            int c = 0;
            double[] pointsums = new double[front.Count()];

            for (int dim = 0; dim < front.First().Length; dim++)
            {
                double[] arr = front.Select(x => x[dim]).ToArray();
                Array.Sort(arr);
                double fmax = bounds[dim % bounds.GetLength(0), 1];
                double fmin = bounds[dim % bounds.GetLength(0), 0];
                int pointIdx = 0;
                foreach (double[] point in front)
                {
                    double d = 0;
                    int pos = Array.BinarySearch(arr, point[dim]);
                    if (pos != 0 && pos != arr.Count() - 1)
                    {
                        d = (arr[pos + 1] - arr[pos - 1]) / (fmax - fmin);
                        pointsums[pointIdx++] += d;
                    }
                }
            }

            foreach (double d in pointsums)
            {
                if (!Double.IsInfinity(d))
                {
                    sum += d;
                    c++;
                }
            }
            return c == 0 ? Double.PositiveInfinity : sum / c;
        }

    }
}