package umontreal.iro.lecuyer.functions;



/**
 * Represents a function computing the average of several functions.
 * Let 
 * f0(x),…, fn-1(x) be a set of n functions.
 * This function represents the average 
 * 

 * 

 * f (x) = ∑i=0n-1fi(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;
   }
}