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;
  
  /**
   * Implements a Beta distribution for purposes of drawing random numbers.
   * The parameters are alpha and beta. See Wikipedia.
   *
   * @author Joseph Ramsey
   */
  public class Beta implements Distribution {
      static final long serialVersionUID = 23L;
  
      /**
       * Ibid.
       */
      private double alpha = 0.5;
  
      /**
       * Ibid.
       */
      private double beta = 0.5;
  
      /**
       * Ibid.
       */
      private Beta() {
          this.alpha = .5;
          this.beta = .5;
      }
  
      /**
       * Generates a simple exemplar of this class to test serialization.
       */
      public static Beta serializableInstance() {
          return new Beta();
      }
  
      /**
       * See interface.
       */
      public double nextRandom() {
          return RandomUtil.getInstance().nextBeta(alpha, beta);
      }
  
      /**
       * The order of parameters is alpha = 0, beta = 1.
       */
      public void setParameter(int index, double value) {
          if (index == 0) {
              alpha = value;
          } else if (index == 1 && value >= 0) {
              beta = value;
          } else {
              throw new IllegalArgumentException("Illegal value: " + value);
          }
      }
  
      /**
       * The order of parameters is alpha = 0, beta = 1.
       */
      public double getParameter(int index) {
          if (index == 0) {
              return alpha;
          } else if (index == 1) {
              return beta;
          } else {
              throw new IllegalArgumentException("Illegal index: " + index);
          }
      }
  
      /**
       * The order of parameters is alpha = 0, beta = 1.
       */
      public String getParameterName(int index) {
          if (index == 0) {
              return "Alpha";
          } else if (index == 1) {
              return "Beta";
          } else {
              throw new IllegalArgumentException("Not a parameter index: " + index);
          }
      }
  
      /**
       * Uh, there are 2 parameters...
       *
       * @return Ibid.
       */
      public int getNumParameters() {
          return 2;
      }
  
      /**
       * Please don't make me say it...
       */
      public String getName() {
          return "Beta";
      }
  
      /**
       * A string representation of the distribution.
       */
      public String toString() {
          return "B(" + alpha + ", " + beta + ")";
      }
  }
  
  
  
  
  