package umontreal.iro.lecuyer.randvar;
import umontreal.iro.lecuyer.rng.*;
import umontreal.iro.lecuyer.probdist.*;


/**
 * This class implements random variate generators for the 
 * Weibull distribution. Its density is
 * 
 * 

 * 

 * f (x) = αλα(x - δ)α-1exp[- (λ(x - δ))α]         for x > δ,
 * 

 * and f (x) = 0 elsewhere, where 
 * α > 0, and 
 * λ > 0.
 * 
 * 

 * The (non-static) nextDouble method simply calls inverseF on the
 * distribution.
 * 
 */
public class WeibullGen extends RandomVariateGen  {
   private double alpha = -1.0;
   private double lambda = -1.0;
   private double delta = -1.0;


   /**
    * Creates a Weibull random variate generator with parameters
    *  α = alpha, λ = lambda and δ =
    *   delta, using stream s.
    * 
    */
   public WeibullGen (RandomStream s, double alpha, double lambda,
                                      double delta)  {
      super (s, new WeibullDist(alpha, lambda, delta));
      setParams (alpha, lambda, delta);
   }


   /**
    * Creates a Weibull random variate generator with parameters
    *  α = alpha, 
    * λ = 1 and 
    * δ = 0, using stream
    *  s.
    * 
    */
   public WeibullGen (RandomStream s, double alpha)  {
      this (s, alpha, 1.0, 0.0);
   }

   
   /**
    * Creates a new generator for the Weibull distribution dist
    *    and stream s.
    * 
    */
   public WeibullGen (RandomStream s, WeibullDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getAlpha(), dist.getLambda(), dist.getDelta());
   } 

   
   /**
    * Uses inversion to generate a new variate from the Weibull
    *    distribution with parameters α = alpha,
    *    λ = lambda, and δ = delta, using
    *    stream s.
    * 
    */
   public static double nextDouble (RandomStream s, double alpha,
                                    double lambda, double delta)  {
       return WeibullDist.inverseF (alpha, lambda, delta, s.nextDouble());
   }
      

   /**
    * Returns the parameter α.
    * 
    */
   public double getAlpha() {
      return alpha;
   }


   /**
    * Returns the parameter λ.
    * 
    */
   public double getLambda() {
      return lambda;
   }


   /**
    * Returns the parameter δ.
    * 
    * 
    */
   public double getDelta() {
      return delta;
   }


   /**
    * Sets the parameters α, λ and δ for this
    *    object.
    * 
    */
   public void setParams (double alpha, double lambda, double delta) {
      if (alpha <= 0.0)
        throw new IllegalArgumentException ("alpha <= 0");
      if (lambda <= 0.0)
        throw new IllegalArgumentException ("lambda <= 0");
      this.alpha  = alpha;
      this.lambda = lambda;
      this.delta  = delta;
   }

}