Package com.singularsys.extensions.djep

Class DifferentiationVisitor

java.lang.Object

com.singularsys.jep.walkers.GenericDoNothingVisitor<String>

com.singularsys.jep.walkers.GenericDeepCopyVisitor<String>

com.singularsys.extensions.djep.DifferentiationVisitor

All Implemented Interfaces:

GenericVisitor<Node,String,ParseException>, JepComponent, Serializable

Direct Known Subclasses:

MatrixDifferentiationVisitor

public class DifferentiationVisitor
extends GenericDeepCopyVisitor<String>

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	Description
protected DJep	djep
protected TreeUtils	tu

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

ft, nf, ot

Constructor Summary

Constructors

Constructor	Description
DifferentiationVisitor()

Method Summary

Modifier and Type	Method	Description
Node	differentiate(Node node, String varName)	Differentiates an expression tree wrt a variable var.
DiffRulesI	getDiffRule(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(PrintStream out)	Prints all the differentiation rules for all functions on specified stream.
Node	visit(ASTConstant node, String varName)	Differentiates a constant.
Node	visit(ASTFunNode node, String varName)	Applies differentiation to a function.
Node	visit(ASTOpNode node, String var)	Now the recursive calls to differentiate the tree
Node	visit(ASTVarNode node, String varName)	Differentiates a variable.

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

getLightWeightInstance, visit

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

childrenHaveChanged, copyChildrenIfNeeded, copyChildrenIfNeeded, makeException

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.singularsys.jep.GenericVisitor

makeException, visitChildren

Field Details

djep

protected DJep djep

tu

protected TreeUtils tu

Constructor Details

DifferentiationVisitor

public DifferentiationVisitor()

Method Details

init

public void init(Jep j)

Description copied from interface: JepComponent

Initialize the component. This method 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 GenericDoNothingVisitor<String>

Parameters:

j - the current Jep instance

getDiffRule

public DiffRulesI getDiffRule(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(PrintStream out)

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

differentiate

public Node differentiate(Node node,
 String varName)
                   throws ParseException

Differentiates an expression tree wrt a variable var.

Parameters:

node - the top node of the expression tree

varName - the name of 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.

IllegalArgumentException

visit

public Node visit(ASTOpNode node,
 String var)
           throws ParseException

Now the recursive calls to differentiate the tree

Specified by:

visit in interface GenericVisitor<Node,String,ParseException>

Overrides:

visit in class GenericDeepCopyVisitor<String>

Parameters:

node - current node

var - context data

Returns:

the result of visiting the node

Throws:

ParseException

visit

public Node visit(ASTFunNode node,
 String varName)
           throws ParseException

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

Specified by:

visit in interface GenericVisitor<Node,String,ParseException>

Overrides:

visit in class GenericDeepCopyVisitor<String>

Parameters:

node - The node of the function.

varName - The variable to differentiate wrt.

Returns:

the result of visiting the node

Throws:

ParseException

isConstantVar

public boolean isConstantVar(XVariable var)

visit

public Node visit(ASTVarNode node,
 String varName)
           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 GenericVisitor<Node,String,ParseException>

Overrides:

visit in class GenericDeepCopyVisitor<String>

Parameters:

node - current node

varName - context data

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 Node visit(ASTConstant node,
 String varName)
           throws ParseException

Differentiates a constant.

Specified by:

visit in interface GenericVisitor<Node,String,ParseException>

Overrides:

visit in class GenericDeepCopyVisitor<String>

Parameters:

node - current node

varName - context data

Returns:

0 derivatives of constants are always zero.

Throws:

ParseException