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


/**
 * This class implements random variate generators for 
 * the fatigue life distribution with location
 * parameter μ, scale parameter β and shape
 * parameter γ.
 * The density function of this distribution is
 * 
 * 

 * 

 * f (x) = [(((x - μ)/β)1/2 + (β/(x - μ))1/2)/(2γ(x - μ))]φ((((x - μ)/β)1/2 - (β/(x - μ))1/2)/γ),        x > μ
 * 

 * where φ is the probability density of the standard normal distribution.
 * 
 */
public class FatigueLifeGen extends RandomVariateGen  {
   protected double mu;
   protected double beta;
   protected double gamma;




   /**
    * Creates a fatigue life random variate generator with
    *   parameters μ = mu, β = beta and γ =
    *   gamma, using stream s.
    * 
    */
   public FatigueLifeGen (RandomStream s, double mu, double beta,
                                          double gamma)  {
      super (s, new FatigueLifeDist(mu, beta, gamma));
      setParams (mu, beta, gamma);
   }


   /**
    * Creates a new generator for the distribution dist,
    *      using stream s.
    * 
    */
   public FatigueLifeGen (RandomStream s, FatigueLifeDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getMu(), dist.getBeta(), dist.getGamma());
   }


   /**
    * Generates a variate from the fatigue life distribution
    *    with location parameter μ, scale parameter β and shape parameter
    *    γ.
    * 
    */
   public static double nextDouble (RandomStream s, double mu, double beta,
                                    double gamma) {
      return FatigueLifeDist.inverseF (mu, beta, gamma, s.nextDouble());
   }


   /**
    * Returns the parameter β of this object.
    * 
    */
   public double getBeta() {
      return beta;
   }


   /**
    * Returns the parameter γ of this object.
    * 
    */
   public double getGamma() {
      return gamma;
   }


   /**
    * Returns the parameter μ of this object.
    * 
    * 
    */
   public double getMu() {
      return mu;
   }


   /**
    * Sets the parameters μ, β and γ of this object.
    * 
    */
   protected void setParams (double mu, double beta, double gamma) {
      if (beta <= 0.0)
         throw new IllegalArgumentException ("beta <= 0");
      if (gamma <= 0.0)
         throw new IllegalArgumentException ("gamma <= 0");
      
      this.mu = mu;
      this.beta = beta;
      this.gamma = gamma;
   }

}