com.singularsys.extensions.djep

Class DifferentiationVisitor

java.lang.Object

com.singularsys.jep.walkers.DoNothingVisitor

com.singularsys.jep.walkers.DeepCopyVisitor

com.singularsys.extensions.djep.DifferentiationVisitor

All Implemented Interfaces:

JepComponent, ParserVisitor, java.io.Serializable

Direct Known Subclasses:

MatrixDifferentiationVisitor

public class DifferentiationVisitor
extends DeepCopyVisitor

A class for performing differentiation of an expression. To use do

 Jep j = ...; Node in = ...;
 DifferentiationVisitor dv = new DifferentiationVisitor(jep);
 dv.addStandardDiffRules();
 Node out = dv.differentiate(in,"x");
 

The class follows the visitor pattern described in ParserVisitor. The rules for differentiating specific functions are contained in object which implement DiffRulesI A number of inner classes which use this interface are defined for specific function types. In particular MacroDiffRules allow the rule for differentiation to be specified by strings. New rules can be added using DJep.addDiffRule(com.singularsys.extensions.djep.DiffRulesI) method.

Author:

R Morris Created on 19-Jun-2003

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected DJep	djep
protected TreeUtils	tu

Fields inherited from class com.singularsys.jep.walkers.DoNothingVisitor

ft, jep, nf, ot, vt

Constructor Summary

Constructors

Constructor and Description
DifferentiationVisitor()

Method Summary

Modifier and Type	Method and Description
Node	differentiate(Node node, java.lang.String var) Differentiates an expression tree wrt a variable var.
DiffRulesI	getDiffRule(java.lang.String name) finds the rule for function with given name.
void	init(Jep j) Initialize the component.
boolean	isConstantVar(XVariable var)
void	printDiffRules() Prints all the differentiation rules for all functions on System.out.
void	printDiffRules(java.io.PrintStream out) Prints all the differentiation rules for all functions on specified stream.
java.lang.Object	visit(ASTConstant node, java.lang.Object data) Differentiates a constant.
java.lang.Object	visit(ASTFunNode node, java.lang.Object data) Applies differentiation to a function.
java.lang.Object	visit(ASTOpNode node, java.lang.Object data) Now the recursive calls to differentiate the tree
java.lang.Object	visit(ASTVarNode node, java.lang.Object data) Differentiates a variable.

Methods inherited from class com.singularsys.jep.walkers.DeepCopyVisitor

deepCopy

Methods inherited from class com.singularsys.jep.walkers.DoNothingVisitor

childrenHaveChanged, copyChildrenIfNeeded, getFunctionTable, getLightWeightInstance, getNodeFactory, getOperatorTable, getVariableTable, visit, visitChildren, visitNode

Methods inherited from class java.lang.Object

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

Field Detail

djep

protected DJep djep

tu

protected TreeUtils tu

Constructor Detail

DifferentiationVisitor

public DifferentiationVisitor()

Method Detail

init

public void init(Jep j)

Description copied from interface: JepComponent

Initialize the component. This methods is called whenever a component is added to Jep. Hence it allows components to keep track of the other components they may rely on.

Specified by:

init in interface JepComponent

Overrides:

init in class DoNothingVisitor

Parameters:

j - the current Jep instance

getDiffRule

public DiffRulesI getDiffRule(java.lang.String name)

finds the rule for function with given name.

printDiffRules

public void printDiffRules()

Prints all the differentiation rules for all functions on System.out.

printDiffRules

public void printDiffRules(java.io.PrintStream out)

Prints all the differentiation rules for all functions on specified stream.

differentiate

public Node differentiate(Node node,
                          java.lang.String var)
                   throws ParseException

Differentiates an expression tree wrt a variable var.

Parameters:

node - the top node of the expression tree

var - the variable to differentiate wrt

Returns:

the top node of the differentiated expression

Throws:

ParseException - if some error occurred while trying to differentiate, for instance of no rule supplied for given function.

java.lang.IllegalArgumentException

visit

public java.lang.Object visit(ASTOpNode node,
                              java.lang.Object data)
                       throws JepException

Now the recursive calls to differentiate the tree

Specified by:

visit in interface ParserVisitor

Overrides:

visit in class DeepCopyVisitor

Throws:

JepException

visit

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

Applies differentiation to a function. Used the rules specified by objects of type DiffRulesI.

Specified by:

visit in interface ParserVisitor

Overrides:

visit in class DeepCopyVisitor

Parameters:

node - The node of the function.

data - The variable to differentiate wrt.

Throws:

JepException

isConstantVar

public boolean isConstantVar(XVariable var)

visit

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

Differentiates a variable. May want to alter behaviour when using multi equation as diff(f,x) might not be zero.

Specified by:

visit in interface ParserVisitor

Overrides:

visit in class DeepCopyVisitor

Returns:

a constant node with value 1 if the variable has the same name as data, 0 if the variable has a different name.

Throws:

ParseException

visit

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

Differentiates a constant.

Specified by:

visit in interface ParserVisitor

Overrides:

visit in class DeepCopyVisitor

Returns:

0 derivatives of constants are always zero.

Throws:

ParseException