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.calculator.expression;
  
  /**
   * Represents an equation of the form Variable = Expression, where the Variable represents
   * a column in some dataset.
   *
   * @author Tyler Gibson
   */
  public class Equation {
  
      /**
       * The string value of the variable.
       */
      private String variable;
  
  
      /**
       * The expression that should be used to evaluate the variables new value.
       */
      private Expression expression;
  
  
      /**
       * The unparsed expression.
       */
      private String unparsedExpression;
  
  
      public Equation(String variable, Expression expression, String unparsed) {
          if (variable == null) {
              throw new NullPointerException("variable was null.");
          }
          if (expression == null) {
              throw new NullPointerException("expression was null.");
          }
          if (unparsed == null) {
              throw new NullPointerException("unparsed was null.");
          }
          this.unparsedExpression = unparsed;
          this.variable = variable;
          this.expression = expression;
      }
  
      //========================== Public Methods ======================//
  
  
      public String getUnparsedExpression() {
          return this.unparsedExpression;
      }
  
  
      public String getVariable() {
          return this.variable;
      }
  
  
      public Expression getExpression() {
          return this.expression;
      }
  
  }
  
  
  
  
  