package umontreal.iro.lecuyer.functions;



/**
 * Represents a function computing 
 * (af (x) + b)p for a user-defined function
 * f (x) and power p.
 * 
 */
public class PowerMathFunction implements MathFunction

,
      MathFunctionWithFirstDerivative {
   private MathFunction func;
   private double a, b;
   private double power;


   /**
    * Constructs a new power function for function func and power
    *  power. The values of the constants are a = 1 and b = 0.
    * 
    * @param func the function f (x).
    * 
    *    @param power the power p.
    * 
    * 
    */
   public PowerMathFunction (MathFunction func, double power) {
      this (func, 1, 0, power);
   }


   /**
    * Constructs a new power function for function func, power
    *  power, and constants a and b.
    * 
    * @param func the function f (x).
    * 
    *    @param power the power p.
    * 
    *    @param a the multiplicative constant.
    * 
    *    @param b the additive constant.
    * 
    * 
    */
   public PowerMathFunction (MathFunction func, double a, double b, double power) {
      if (func == null)
         throw new NullPointerException ();
      this.func = func;
      this.a = a;
      this.b = b;
      this.power = power;
   }


   /**
    * Returns the function f (x).
    * 
    * @return the function.
    * 
    */
   public MathFunction getFunction () {
      return func;
   }


   /**
    * Returns the value of a.
    * 
    * @return the value of a.
    * 
    */
   public double getA () {
      return a;
   }


   /**
    * Returns the value of b.
    * 
    * @return the value of b.
    * 
    */
   public double getB () {
      return b;
   }


   /**
    * Returns the power p.
    * 
    * @return the power.
    * 
    */
   public double getPower () {
      return power;
   }


   public double derivative (double x) {
      final double fder = MathFunctionUtil.derivative (func, x);
      return getA()*getPower()*Math.pow (getA() * func.evaluate (x) + getB(), getPower() - 1)*fder;
   }

   public double evaluate (double x) {
      final double v = func.evaluate (x);
      return Math.pow (a * v + b, power);
   }
}