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


/**
 * This class implements random variate generators for 
 * the inverse Gaussian distribution with location parameter
 * μ > 0 and scale parameter 
 * λ > 0.
 * The density function of this distribution is
 * 
 * 

 * 

 * f (x) = (λ)1/2/(2πx3)  e-λ(x-μ)2/(2μ2x)         for x > 0.
 * 

 * 
 */
public class InverseGaussianGen extends RandomVariateGen  {
   protected double mu = -1.0;
   protected double lambda = -1.0;




   /**
    * Creates an inverse Gaussian random variate generator
    *  with parameters μ = mu and λ = lambda,
    *   using stream s.
    * 
    */
   public InverseGaussianGen (RandomStream s, double mu, double lambda)  {
      super (s, new InverseGaussianDist(mu, lambda));
      setParams (mu, lambda);
   }


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


   /**
    * Generates a variate from the inverse gaussian distribution
    *    with location parameter μ > 0 and scale parameter 
    * λ > 0.
    * 
    */
   public static double nextDouble (RandomStream s,
                                    double mu, double lambda) {
      return InverseGaussianDist.inverseF (mu, lambda, s.nextDouble());
   }


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


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


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

}