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


/**
 * Implements Pascal random variate generators, which is a special case of the
 * negative binomial generator with parameter γ equal to a positive integer.
 * See {@link NegativeBinomialGen} for a description.
 * 
 */
public class PascalGen extends RandomVariateGenInt  {
   protected int    n;
   protected double p;    



   /**
    * Creates a Pascal random variate generator with parameters n and p,
    *   using stream s.
    * 
    */
   public PascalGen (RandomStream s, int n, double p) {
      super (s, new PascalDist (n, p));
      setParams (n, p);
   }


   /**
    * Creates a new generator for the distribution dist, using
    *   stream s.
    * 
    */
   public PascalGen (RandomStream s, PascalDist dist) {
      super (s, dist);
      if (dist != null)
         setParams (dist.getN(), dist.getP());
   }

    
   /**
    * Generates a new variate from the Pascal distribution,
    *  with parameters n = n and p = p, using stream s.
    * 
    */
   public static int nextInt (RandomStream s, int n, double p) {
      return PascalDist.inverseF (n, p, s.nextDouble());
   }


   /**
    * Returns the parameter n of this object.
    * 
    */
   public int getN() {
      return n;
   }
   


   /**
    * Returns the parameter p of this object.
    * 
    * 
    */
   public double getP() {
      return p;
   }
   


   /**
    * Sets the parameter n and p of this object.
    * 
    */
   protected void setParams (int n, double p) {
      if (p < 0.0 || p > 1.0)
         throw new IllegalArgumentException ("p not in [0, 1]");
      if (n <= 0)
         throw new IllegalArgumentException ("n <= 0");
      this.p = p;
      this.n = n;
   }

}