/*
* 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 weka.core.parser.java_cup.runtime.DefaultSymbolFactory;
import weka.core.parser.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 < 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: 1.8 $
*/
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: 1.8 $");
}
}