MathematicalExpression.java

/*
 *   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 3 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, see <http://www.gnu.org/licenses/>.
 */

/*
 *    MathematicalExpression.java
 *    Copyright (C) 2008-2012 University of Waikato, Hamilton, New Zealand
 */

package weka.core;

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 < expr
 *               | expr <= expr
 *               | expr > expr
 *               | expr >= 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: 8034 $
 */
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();*/
		return 0.0;
	}

	/**
	 * Returns the revision string.
	 * 
	 * @return the revision
	 */
	public String getRevision() {
		return RevisionUtils.extract("$Revision: 8034 $");
	}
}