weka.core

Class MathematicalExpression

java.lang.Object

weka.core.MathematicalExpression

All Implemented Interfaces:

RevisionHandler

public class MathematicalExpression
extends java.lang.Object
implements RevisionHandler

Class for evaluating a string adhering the following grammar:

 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
               ;
 

Code example 1:

 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);
 

Code Example 2 (uses the "ifelse" construct):

 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);
 }
 

Version:

$Revision: 4942 $

Author:

FracPete (fracpete at waikato dot ac dot nz)

Constructor Summary

Constructors

Constructor and Description
MathematicalExpression()

Method Summary

Modifier and Type	Method and Description
static double	evaluate(java.lang.String expr, java.util.HashMap symbols) Parses and evaluates the given expression.
java.lang.String	getRevision() Returns the revision string.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MathematicalExpression

public MathematicalExpression()

Method Detail

evaluate

public static double evaluate(java.lang.String expr,
                              java.util.HashMap symbols)
                       throws java.lang.Exception

Parses and evaluates the given expression. Returns the result of the mathematical expression, based on the given values of the symbols.

Parameters:

expr - the expression to evaluate

symbols - the symbol/value mapping

Returns:

the evaluated result

Throws:

java.lang.Exception - if something goes wrong

getRevision

public java.lang.String getRevision()

Returns the revision string.

Specified by:

getRevision in interface RevisionHandler

Returns:

the revision