org.lsmp.djep.xjep
Class SimplificationVisitor

java.lang.Object
  org.lsmp.djep.xjep.DoNothingVisitor
      org.lsmp.djep.xjep.SimplificationVisitor

All Implemented Interfaces:

ParserVisitor

public class SimplificationVisitor
extends DoNothingVisitor

Simplifies an expression. To use

 JEP j = ...; Node in = ...;
 SimplificationVisitor sv = new SimplificationVisitor(tu);
 Node out = sv.simplify(in);
 

Its intended to completly rewrite this class to that simplification rules can be specified by strings in a way similar to DiffRulesI. It also would be nice to change the rules depending on the type of arguments, for example matrix multiplication is not commutative. But some of the in built rules exploit commutativity.

Author:

Rich Morris Created on 20-Jun-2003 TODO cope with 'a - (-1) * b' TODO cope with '0 - uminus(b)' TODO cope with simplifying complex numbers

Constructor Summary

SimplificationVisitor()

Method Summary

Node	simplify(Node node, XJep xjep) must be implemented for subclasses.
Node	simplifyAdd(Node lhs, Node rhs) Simplifies an addition.
Node	simplifyBuiltOperatorNode(Operator op, Node lhs, Node rhs) First create a new node and then simplify it.
Node	simplifyDivide(Node child1, Node child2) Simplifies a division.
Node	simplifyMultiply(Node child1, Node child2) Simplifies a multiplication.
Node	simplifyOp(ASTFunNode node, Node[] children) simplifies operators, does not descend into children
Node	simplifyPower(Node child1, Node child2) Simplify a power.
Node	simplifySubtract(Node lhs, Node rhs) Simplifies a subtraction.
Node	simplifyTripple(XOperator op, Node lhs, Node rhs) Simplifies expressions like 2+(3+x) or (2+x)+3
java.lang.Object	visit(ASTFunNode node, java.lang.Object data)

Methods inherited from class org.lsmp.djep.xjep.DoNothingVisitor

acceptChildrenAsArray, visit, visit, visit, visit

Methods inherited from class java.lang.Object

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

Constructor Detail

SimplificationVisitor

public SimplificationVisitor()

Method Detail

simplify

public Node simplify(Node node,
                     XJep xjep)
              throws ParseException,
                     java.lang.IllegalArgumentException

must be implemented for subclasses.

Throws:

ParseException

java.lang.IllegalArgumentException

simplifyBuiltOperatorNode

public Node simplifyBuiltOperatorNode(Operator op,
                                      Node lhs,
                                      Node rhs)
                               throws ParseException

First create a new node and then simplify it.

Throws:

ParseException

simplifyTripple

public Node simplifyTripple(XOperator op,
                            Node lhs,
                            Node rhs)
                     throws ParseException

Simplifies expressions like 2+(3+x) or (2+x)+3

Parameters:

op - the root operator

lhs - the left hand side node

rhs - the right hand side node

Returns:

null if no rewrite happens or top node or top node of new tree.

Throws:

ParseException

simplifyAdd

public Node simplifyAdd(Node lhs,
                        Node rhs)
                 throws ParseException

Simplifies an addition. Performs the following rules

 0+x -> x
 x+0 -> x
 m+n -> (m+n) where m,n are numbers
 x - (-2) -> x + 2 for any negative number -2
 x + (-2) -> x - 2 for any negative number -2
 2 +/- ( 3 +/- x ) ->  (2 +/- 3 ) +/- x and similar
 

Throws:

ParseException

simplifySubtract

public Node simplifySubtract(Node lhs,
                             Node rhs)
                      throws ParseException

Simplifies a subtraction. Performs the following rules

 0-x -> 0-x
 x-0 -> x
 m-n -> (m-n) where m,n are numbers
 x - (-2) -> x + 2 for any negative number -2
 x + (-2) -> x - 2 for any negative number -2
 2 +/- ( 3 +/- x ) ->  (2 +/- 3 ) +/- x and similar
 

Parameters:

lhs - the left hand side

rhs - the right hand side

Throws:

ParseException

simplifyMultiply

public Node simplifyMultiply(Node child1,
                             Node child2)
                      throws ParseException

Simplifies a multiplication.

 0 * Inf -> NaN
 0 * x -> 0
 x * 0 -> 0
 1 * x -> x
 x * 1 -> x
 Inf * x -> Inf
 x * Inf -> Inf
 2 * ( 3 * x) -> (2*3) * x
 and similar.
 

Throws:

ParseException

simplifyDivide

public Node simplifyDivide(Node child1,
                           Node child2)
                    throws ParseException

Simplifies a division.

 0/0 -> NaN
 0/Inf -> Inf
 0/x -> Inf
 x/0 -> Inf
 x/1 -> x
 Inf / x -> Inf
 x / Inf -> 0
 2 / ( 3 * x) -> (2/3) / x
 2 / ( x * 3) -> (2/3) / x
 2 / ( 3 / x) -> (2/3) * x
 2 / ( x / 3) -> (2*3) / x
 (2 * x) / 3 -> (2/3) * x
 (x * 2) / 3 -> x * (2/3)
 (2 / x) / 3 -> (2/3) / x
 (x / 2) / 3 -> x / (2*3)
 

Throws:

ParseException

simplifyPower

public Node simplifyPower(Node child1,
                          Node child2)
                   throws ParseException

Simplify a power.

 x^0 -> 1
 x^1 -> x
 0^0 -> NaN
 0^x -> 0
 1^x -> 1
 

Throws:

ParseException

simplifyOp

public Node simplifyOp(ASTFunNode node,
                       Node[] children)
                throws ParseException

simplifies operators, does not descend into children

Throws:

ParseException

visit

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

Specified by:

visit in interface ParserVisitor

Overrides:

visit in class DoNothingVisitor

Throws:

ParseException