code: ///////////////////////////////////////////////////////////////////////////////
  // For information as to what this class does, see the Javadoc, below.       //
  // Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,       //
  // 2007, 2008, 2009, 2010, 2014, 2015 by Peter Spirtes, Richard Scheines, Joseph   //
  // Ramsey, and Clark Glymour.                                                //
  //                                                                           //
  // This program is free software; you can redistribute it and/or modify      //
  // it under the terms of the GNU General Public License as published by      //
  // the Free Software Foundation; either version 2 of the License, or         //
  // (at your option) any later version.                                       //
  //                                                                           //
  // This program is distributed in the hope that it will be useful,           //
  // but WITHOUT ANY WARRANTY; without even the implied warranty of            //
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the             //
  // GNU General Public License for more details.                              //
  //                                                                           //
  // You should have received a copy of the GNU General Public License         //
  // along with this program; if not, write to the Free Software               //
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA //
  ///////////////////////////////////////////////////////////////////////////////
  
  package edu.cmu.tetrad.util.dist;
  
  import edu.cmu.tetrad.util.RandomUtil;
  
  /**
   * Wraps a chi square distribution for purposes of drawing random samples.
   * Methods are provided to allow parameters to be manipulated in an interface.
   *
   * @author Joseph Ramsey
   */
  public class Poisson implements Distribution {
      static final long serialVersionUID = 23L;
  
      private double mean;
  
      private Poisson() {
          this.mean = (double) 1;
      }
  
      /**
       * Generates a simple exemplar of this class to test serialization.
       *
       * @return The exemplar.
       */
      public static Poisson serializableInstance() {
          return new Poisson();
      }
  
      public int getNumParameters() {
          return 1;
      }
  
      public String getName() {
          return "Distibution";
      }
  
      public void setParameter(int index, double value) {
          if (index == 0) {
              mean = value;
          }
  
          throw new IllegalArgumentException();
      }
  
      public double getParameter(int index) {
          if (index == 0) {
              return mean;
          }
  
          throw new IllegalArgumentException();
      }
  
      public String getParameterName(int index) {
          if (index == 0) {
              return "Mean";
          }
  
          throw new IllegalArgumentException();
      }
  
      public double nextRandom() {
          return RandomUtil.getInstance().nextPoisson(mean);
      }
  
      public String toString() {
          return "Poisson(" + mean + ")";
      }
  }
  
  
  
  
  