source: trunk/sources/HeuristicLab.Functions/Division.cs @ 205

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2008 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;
using System.Collections.Generic;
using System.Text;
using HeuristicLab.Core;
using System.Diagnostics;
using HeuristicLab.Constraints;
using System.Linq;
using HeuristicLab.DataAnalysis;

namespace HeuristicLab.Functions {
  public class Division : FunctionBase {
    private const double EPSILON = 10.0E-20; // if any divisor is < EPSILON return 0

    public override string Description {
      get {
        return @"Protected division
Divides the result of the first sub-tree by the results of the following sub-tree.
In case one of the divisors is 0 returns 0.
    (/ 3) => 1/3
    (/ 2 3) => 2/3
    (/ 3 4 5) => 3/20
    (/ 2 0 4) => 0
";
      }
    }

    public Division()
      : base() {
      // 2 - 3 seems like an reasonable defaut (used for +,-,*,/) (discussion with swinkler and maffenze)
      AddConstraint(new NumberOfSubOperatorsConstraint(2, 3));
    }

    public override double Apply(Dataset dataset, int sampleIndex, double[] args) {
      // (/ 3) => 1/3
      // (/ 2 3) => 2/3
      // (/ 3 4 5) => 3/20

      if(args.Length == 1) {
        double divisor = args[0];
        if(Math.Abs(divisor) < EPSILON) return 0;
        else return 1.0 / divisor;
      } else {
        double result = args[0];
        for(int i = 1; i < args.Length; i++) {
          double divisor = args[i];
          if(Math.Abs(divisor) < EPSILON) return 0.0;
          result /= divisor;
        }
        return result;
      }
    }

    public override void Accept(IFunctionVisitor visitor) {
      visitor.Visit(this);
    }
  }
}