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.NumberFormatUtil;
  import edu.cmu.tetrad.util.RandomUtil;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.text.NumberFormat;
  
  /**
   * 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
   */
  @SuppressWarnings({"WeakerAccess"})
  public class Split implements Distribution {
      static final long serialVersionUID = 23L;
  
      /**
       * @serial
       */
      private double a;
  
      /**
       * @serial
       */
      private double b;
  
      //===========================CONSTRUCTORS===========================//
  
      /**
       * Creates a new split distribution, drawing uniformly from [-b, -a] U [a, b], where a and
       * b are positive real numbers.
       *
       * @param a Ibid.
       * @param b Ibid.
       */
      public Split(double a, double b) {
          if (a < 0) {
              throw new IllegalArgumentException(
                      "When asking for a range from a to b, the value of a must be >= 0: a = " + a + " b = " + b);
          }
  
          if (b <= a) {
              throw new IllegalArgumentException(
                      "When asking for a range from a to b, the value of b must be > a: a = " + a + " b = " + b);
          }
  
          this.a = a;
          this.b = b;
      }
  
      /**
       * Generates a simple exemplar of this class to test serialization.
       *
       * @return the exemplar.
       */
      public static Split serializableInstance() {
          return new Split(0.5, 1.5);
      }
  
      //==========================PUBLIC METHODS==========================//
  
      /**
       * @return a random value from [-b, -a] U [a, b].
       */
      public double nextRandom() {
          double c = RandomUtil.getInstance().nextDouble();
          double value = getA() + c * (getB() - getA());
  
          if (RandomUtil.getInstance().nextDouble() < 0.5) {
              value *= -1.0;
          }
  
          return value;
      }
  
      public double getA() {
          return a;
      }
  
      public double getB() {
          return b;
      }
  
  
      public String getName() {
          return "Split Distribution";
      }
  
      public String toString() {
          NumberFormat nf = NumberFormatUtil.getInstance().getNumberFormat();
          return "Split(" + nf.format(a) + ", " + nf.format(b) + ", " + ")";
      }
  
  
      public void setParameter(int index, double value) {
          if (index == 0 && value < b) {
              a = value;
          } else if (index == 1 && value > a) {
              b = value;
          } else {
              throw new IllegalArgumentException("Cannot set value of " + index + " to " + value);
          }
      }
  
      public double getParameter(int index) {
          if (index == 0) {
              return a;
          } else if (index == 1) {
              return b;
          } else {
              throw new IllegalArgumentException("There is no parameter " + index);
          }
      }
  
      public String getParameterName(int index) {
          if (index == 0) {
              return "Lower bound (> 0)";
          } else if (index == 1) {
              return "Upper bound (> 0)";
          } else {
              throw new IllegalArgumentException("Not a parameter index: " + index);
          }
      }
  
      public int getNumParameters() {
          return 2;
      }
  
      /**
       * Adds semantic checks to the default deserialization method. This method
       * must have the standard signature for a readObject method, and the body of
       * the method must begin with "s.defaultReadObject();". Other than that, any
       * semantic checks can be specified and do not need to stay the same from
       * version to version. A readObject method of this form may be added to any
       * class, even if Tetrad sessions were previously saved out using a version
       * of the class that didn't include it. (That's what the
       * "s.defaultReadObject();" is for. See J. Bloch, Effective Java, for help.
       *
       * @param s the stream to read from.
       * @throws java.io.IOException    If the stream cannot be read.
       * @throws ClassNotFoundException If the class of an object in the stream is not
       *                                in the project.
       */
      private void readObject(ObjectInputStream s)
              throws IOException, ClassNotFoundException {
          s.defaultReadObject();
  
          if (a < 0) {
              throw new IllegalStateException();
          }
  
          if (b <= a) {
              throw new IllegalStateException();
          }
      }
  }
  
  
  
  
  