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SSJ is a Java library for stochastic simulation, developed under the direction of Pierre L'Ecuyer, in the Département d'Informatique et de Recherche Opérationnelle (DIRO), at the Université de Montréal. It provides facilities for generating uniform and nonuniform random variates, computing different measures related to probability distributions, performing goodness-of-fit tests, applying quasi-Monte Carlo methods, collecting (elementary) statistics, and programming discrete-event simulations with both events and processes.

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/*
 * Class:        AverageMathFunction
 * Description:  
 * Environment:  Java
 * Software:     SSJ 
 * Copyright (C) 2001  Pierre L'Ecuyer and Université de Montréal
 * Organization: DIRO, Université de Montréal
 * @author       Éric Buist
 * @since

 * SSJ is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License (GPL) as published by the
 * Free Software Foundation, either version 3 of the License, or
 * any later version.

 * SSJ 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.

 * A copy of the GNU General Public License is available at
   GPL licence site.
 */

package umontreal.iro.lecuyer.functions;



/**
 * Represents a function computing the average of several functions.
 * Let 
 * f₀(x),…, f_n-1(x) be a set of n functions.
 * This function represents the average 
 * 
 * 
 * f (x) = ∑_i=0^n-1f_i(x).
 * 

 * 
 */
public class AverageMathFunction implements MathFunction

,
   MathFunctionWithFirstDerivative, MathFunctionWithDerivative,
   MathFunctionWithIntegral {
   private MathFunction[] func;


   /**
    * Constructs a function computing the average
    *  of the functions in the array func.
    * 
    * @param func the array of functions to average.
    * 
    * 
    */
   public AverageMathFunction (MathFunction... func) {
      if (func == null)
         throw new NullPointerException();
      this.func = func.clone ();
   }


   /**
    * Returns the functions being averaged.
    * 
    * @return the averaged functions.
    * 
    */
   public MathFunction[] getFunctions() {
      return func.clone ();
   }


   public double evaluate (double x) {
      double sum = 0;
      for (final MathFunction fi : func)
         sum += fi.evaluate (x);
      return sum / func.length;
   }
   
   public double derivative (double x, int n) {
      if (n < 0)
         throw new IllegalArgumentException ("n must be greater than or equal to 0");
      if (n == 0)
         return evaluate (x);
      double sum = 0;
      for (final MathFunction fi : func)
         sum += MathFunctionUtil.derivative (fi, x, n);
      return sum / func.length;
   }

   public double derivative (double x) {
      double sum = 0;
      for (final MathFunction fi : func)
         sum += MathFunctionUtil.derivative (fi, x);
      return sum / func.length;
   }

   public double integral (double a, double b) {
      double sum = 0;
      for (final MathFunction fi : func)
         sum += MathFunctionUtil.integral (fi, a, b);
      return sum / func.length;
   }
}