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


/**
 * Implements Pascal random variate generators by
 * the convolution method.
 * The method generates n geometric variates with probability p
 * and adds them up.
 * 
 * 

 * The algorithm is slow if n is large.
 * 
 */
public class PascalConvolutionGen extends PascalGen  {



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


   /**
    * Creates a new generator for the distribution dist, using
    *   stream s.
    * 
    */
   public PascalConvolutionGen (RandomStream s, PascalDist dist) {
      super (s, dist);
   }
 
    
   public int nextInt() {
      int x = 0;
      for (int i = 0; i < n; i++)
         x += GeometricDist.inverseF (p, stream.nextDouble());
      return x;

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


   private static int convolution (RandomStream stream, int n, double p) {
      int x = 0;
      for (int i = 0; i < n; i++)
         x += GeometricDist.inverseF (p, stream.nextDouble());
      return x;
   }
}