source: branches/DataAnalysis/HeuristicLab.Problems.DataAnalysis/3.3/Evaluators/OnlineCovarianceEvaluator.cs @ 4501

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2010 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
 *
 * This file is part of HeuristicLab.
 *
 * HeuristicLab is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * HeuristicLab is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
 */
#endregion

using System;

namespace HeuristicLab.Problems.DataAnalysis.Evaluators {
  public class OnlineCovarianceEvaluator : IOnlineEvaluator {

    private double xMean, yMean, Cn;
    private int n;
    public double Covariance {
      get {
        if (n < 1)
          throw new InvalidOperationException("No elements");
        else
          return Cn / n;
      }
    }

    public OnlineCovarianceEvaluator() {
      Reset();
    }

    #region IOnlineEvaluator Members
    public double Value {
      get { return Covariance; }
    }
    public void Reset() {
      n = 0;
      Cn = 0.0;
      xMean = 0.0;
      yMean = 0.0;
    }

    public void Add(double x, double y) {
      if (double.IsNaN(x) || double.IsInfinity(x) ||
          double.IsNaN(y) || double.IsInfinity(y)) {
        throw new ArgumentException("Covariance is not defined for series containing NaN or infinity elements");
      } else {
        n++;
        // online calculation of tMean

        xMean = xMean + (x - xMean) / n;
        double deltaY = y - yMean; // delta = (y - yMean(n-1))
        yMean = yMean + deltaY / n;

        // online calculation of covariance
        Cn = Cn + deltaY * (x - xMean); // C(n) = C(n-1) + (y - yMean(n-1)) (x - xMean(n))
      }
    }
    #endregion
  }
}