org.lsmp.djep.rpe
Class RpEval

java.lang.Object
  org.lsmp.djep.rpe.RpEval

All Implemented Interfaces:

ParserVisitor

public final class RpEval
extends java.lang.Object
implements ParserVisitor

A fast evaluation algorithm for equations over Doubles, does not work with vectors or matricies. This is based around reverse polish notation and is optimised for speed at every opportunity.

To use do

 JEP j = ...;
 Node node = ...; 
 RpEval rpe = new RpEval(j);
 RpCommandList list = rpe.compile(node);
 double val = rpe.evaluate(list);
 System.out.println(val);
 rpe.cleanUp();
 

The compile methods converts the expression represented by node into a string of commands. For example the expression "1+2*3" will be converted into the sequence of commands

 Constant no 1 (pushes constant onto stack)
 Constant no 2
 Constant no 3
 Multiply scalers (multiplies last two entries on stack)
 Add scalers (adds last two entries on stack)
 

The evaluate method executes these methods sequentially using a stack and returns the last object on the stack.

A few cautionary notes: Its very unlikely to be thread safe. It only works over doubles expressions with complex numbers or strings will cause problems. It only works for expressions involving scalers.

Implementation notes A lot of things have been done to make it as fast as possible:

• Everything is final which maximises the possibility for in-lining.
• All object creation happens during compile.
• All calculations done using double values.
• Each operator/function is hand coded. To extend functionality you will have to modify the source.

Author:

Rich Morris Created on 14-Apr-2004

Constructor Summary

RpEval(JEP jep)

Method Summary

void	cleanUp() Removes observers and other cleanup needed when evaluator no longer used.
RpCommandList	compile(Node node) Compile the expressions to produce a set of commands in reverse Polish notation.
double	evaluate(RpCommandList comList) Evaluate the expression.
java.lang.Object	visit(ASTConstant node, java.lang.Object data)
java.lang.Object	visit(ASTFunNode node, java.lang.Object data)
java.lang.Object	visit(ASTStart node, java.lang.Object data)
java.lang.Object	visit(ASTVarNode node, java.lang.Object data)
java.lang.Object	visit(SimpleNode node, java.lang.Object data)

Methods inherited from class java.lang.Object

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

Constructor Detail

RpEval

public RpEval(JEP jep)

Method Detail

compile

public final RpCommandList compile(Node node)
                            throws ParseException

Compile the expressions to produce a set of commands in reverse Polish notation.

Throws:

ParseException

visit

public final java.lang.Object visit(ASTStart node,
                                    java.lang.Object data)
                             throws ParseException

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public final java.lang.Object visit(SimpleNode node,
                                    java.lang.Object data)
                             throws ParseException

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public final java.lang.Object visit(ASTConstant node,
                                    java.lang.Object data)
                             throws ParseException

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public final java.lang.Object visit(ASTVarNode node,
                                    java.lang.Object data)
                             throws ParseException

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

visit

public final java.lang.Object visit(ASTFunNode node,
                                    java.lang.Object data)
                             throws ParseException

Specified by:

visit in interface ParserVisitor

Throws:

ParseException

evaluate

public final double evaluate(RpCommandList comList)

Evaluate the expression.

Returns:

the double value of the equation

cleanUp

public void cleanUp()

Removes observers and other cleanup needed when evaluator no longer used.