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;
  
  import java.util.Arrays;
  
  /**
   * Wraps a chi square distribution for purposes of drawing random samples.
   * Methods are provided to allow parameters to be manipulated in an interface.
   * A value of n is returned if a number drawn uniformly from [0, 1] is less
   * than the n + 1th p value.
   *
   * @author Joseph Ramsey
   */
  public class Discrete implements Distribution {
      static final long serialVersionUID = 23L;
  
      private final double[] p;
  
      /**
       * A discrete distribution with 0 with probability 1 - p and 1 with probability p. Each of the
       * supplied values must be in (0, 1), and each must be less than its
       * successor (if it has one).
       */
      private Discrete(double... p) {
          this.p = convert(p);
      }
  
      /**
       * Generates a simple exemplar of this class to test serialization.
       *
       * @return The exemplar.
       */
      @SuppressWarnings({"UnusedDeclaration"})
      public static Discrete serializableInstance() {
          return new Discrete(.1, .4, .9);
      }
  
      public int getNumParameters() {
          return p.length;
      }
  
      public String getName() {
          return "Discrete";
      }
  
      public void setParameter(int index, double value) {
          p[index] = value;
      }
  
      public double getParameter(int index) {
          return p[index];
      }
  
      public String getParameterName(int index) {
          return "Cut #" + (index + 1);
      }
  
      public double nextRandom() {
          double r = RandomUtil.getInstance().nextDouble();
  
          for (int i = 0; i < p.length; i++) {
              if (r < p[i]) return i;
          }
  
          throw new IllegalArgumentException();
      }
  
      public String toString() {
          return "Discrete(" + Arrays.toString(p) + ")";
      }
  
      //=============================PRIVATE METHODS=========================//
  
      private double[] convert(double... p) {
          for (double _p : p) {
              if (_p < 0) throw new IllegalArgumentException("All arguments must be >= 0: " + _p);
          }
  
          double sum = 0.0;
  
          for (double _p : p) {
              sum += _p;
          }
  
          for (int i = 0; i < p.length; i++) {
              p[i] = p[i] /= sum;
          }
  
          for (int i = 1; i < p.length; i++) {
              p[i] = p[i - 1] + p[i];
          }
  
          return p;
      }
  }
  
  
  
  