content: /*
   *    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., 675 Mass Ave, Cambridge, MA 02139, USA.
   */
  
  /*
   *    MathematicalExpression.java
   *    Copyright (C) 2008 University of Waikato, Hamilton, New Zealand
   */
  
  package weka.core;
  
  import weka.core.mathematicalexpression.Parser;
  import weka.core.mathematicalexpression.Scanner;
  import java_cup.runtime.DefaultSymbolFactory;
  import java_cup.runtime.SymbolFactory;
  
  import java.io.ByteArrayInputStream;
  import java.util.HashMap;
  
  /** 
   * Class for evaluating a string adhering the following grammar:<br/>
   * 
   * <pre>
   * expr_list ::= expr_list expr_part | expr_part ;
   * expr_part ::= expr ;
   * expr      ::=   NUMBER
   *               | ( expr )
   *               | opexpr
   *               | varexpr
   *               | funcexpr
   *               ;
   * 
   * opexpr    ::=   expr + expr
   *               | expr - expr
   *               | expr * expr
   *               | expr / expr
   *               ;
   * 
   * varexpr  ::=  VARIABLE ;
   * 
   * funcexpr ::=    abs ( expr )
   *               | sqrt ( expr )
   *               | log ( expr )
   *               | exp ( expr )
   *               | sin ( expr )
   *               | cos ( expr )
   *               | tan ( expr )
   *               | rint ( expr )
   *               | floor ( expr )
   *               | pow ( expr , expr )
   *               | ceil ( expr )
   *               | ifelse ( boolexpr , expr (if true) , expr (if false) )
   *               ;
   * 
   * boolexpr ::=    BOOLEAN
   *               | true
   *               | false
   *               | expr &lt; expr
   *               | expr &lt;= expr
   *               | expr &gt; expr
   *               | expr &gt;= expr
   *               | expr = expr
   *               | ( boolexpr )
   *               | ! boolexpr
   *               | boolexpr & boolexpr
   *               | boolexpr | boolexpr
   *               ;
   * </pre>
   *
   * Code example 1:
   * <pre>
   * String expr = "pow(BASE,EXPONENT)*MULT";
   * HashMap symbols = new HashMap();
   * symbols.put("BASE", new Double(2));
   * symbols.put("EXPONENT", new Double(9));
   * symbols.put("MULT", new Double(0.1));
   * double result = MathematicalExpression.evaluate(expr, symbols);
   * System.out.println(expr + " and " + symbols + " = " + result);
   * </pre>
   * 
   * Code Example 2 (uses the "ifelse" construct):
   * <pre>
   * String expr = "ifelse(I<0,pow(BASE,I*0.5),pow(BASE,I))";
   * MathematicalExpression.TreeNode tree = MathematicalExpression.parse(expr);
   * HashMap symbols = new HashMap();
   * symbols.put("BASE", new Double(2));
   * for (int i = -10; i <= 10; i++) {
   *   symbols.put("I", new Double(i));
   *   double result = MathematicalExpression.evaluate(expr, symbols);
   *   System.out.println(expr + " and " + symbols + " = " + result);
   * }
   * </pre>
   *
   * @author FracPete (fracpete at waikato dot ac dot nz)
   * @version $Revision: 4939 $
   */
  public class MathematicalExpression
    implements RevisionHandler {
    
    /**
     * Parses and evaluates the given expression.
     * Returns the result of the mathematical expression, based on the given 
     * values of the symbols.
     * 
     * @param expr	the expression to evaluate
     * @param symbols	the symbol/value mapping
     * @return		the evaluated result
     * @throws Exception	if something goes wrong
     */
    public static double evaluate(String expr, HashMap symbols) throws Exception {
      SymbolFactory 		sf;
      ByteArrayInputStream 	parserInput;
      Parser 			parser;
      
      sf          = new DefaultSymbolFactory();
      parserInput = new ByteArrayInputStream(expr.getBytes());
      parser      = new Parser(new Scanner(parserInput, sf), sf);
      parser.setSymbols(symbols);
      parser.parse();
      
      return parser.getResult();
    }
    
    /**
     * Returns the revision string.
     * 
     * @return		the revision
     */
    public String getRevision() {
      return RevisionUtils.extract("$Revision: 4939 $");
    }
  }
  