NegativeBinomialGen.java

/*
 * Class:        NegativeBinomialGen
 * Description:  random variate generators for the negative binomial distribution
 * Environment:  Java
 * Software:     SSJ 
 * Copyright (C) 2001  Pierre L'Ecuyer and Universite de Montreal
 * Organization: DIRO, Universite de Montreal
 * @author       
 * @since
 *
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
package umontreal.ssj.randvar;
 
import umontreal.ssj.rng.*;
import umontreal.ssj.probdist.*;

public class NegativeBinomialGen extends RandomVariateGenInt {
   protected double gamma;
   protected double p;

   public NegativeBinomialGen(RandomStream s, double gamma, double p) {
      super(s, new NegativeBinomialDist(gamma, p));
      setParams(gamma, p);
   }

   public NegativeBinomialGen(RandomStream s, NegativeBinomialDist dist) {
      super(s, dist);
      if (dist != null)
         setParams(dist.getGamma(), dist.getP());
   }

   public static int nextInt(RandomStream s, double gamma, double p) {
      return NegativeBinomialDist.inverseF(gamma, p, s.nextDouble());
   }

   public double getGamma() {
      return gamma;
   }

   public double getP() {
      return p;
   }

   protected void setParams(double gamma, double p) {
      if (p < 0.0 || p > 1.0)
         throw new IllegalArgumentException("p not in [0, 1]");
      if (gamma <= 0.0)
         throw new IllegalArgumentException("gamma <= 0");
      this.p = p;
      this.gamma = gamma;
   }
}