uk.ac.starlink.ttools.jel

Class JELFunction

java.lang.Object

uk.ac.starlink.ttools.jel.JELFunction

All Implemented Interfaces:

java.util.function.DoubleUnaryOperator

public class JELFunction
extends Object
implements java.util.function.DoubleUnaryOperator

Provides a double precision function of one double precision variable which can be evaluated using JEL. The variable name and an expression giving the result in terms of that variable name are supplied.

Instances of this class are not threadsafe, but could be made so by putting a lock on the evaluate(double) method.

Since:

14 Jun 2012

Author:

Mark Taylor

Constructor Summary

Constructors

Constructor and Description
JELFunction(String xvarname, String fexpr) Constructs a function with no external constants.
JELFunction(String xvarname, String fexpr, Map<String,? extends Constant<?>> constMap) Constructs a function that can reference provided constants.

Method Summary

Modifier and Type	Method and Description
double	applyAsDouble(double x) Does exactly the same as evaluate(double).
double	evaluate(double x) Evaluates this function at a given value of the independent variable.
String	getExpression() Returns the text of the function expression.
Constant<?>[]	getReferencedConstants() Returns an array of any constants that were referenced in this function's expression.
String	getXVarName() Returns the name of the independent variable.
static void	main(String[] args) Main method tests this class.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.function.DoubleUnaryOperator

andThen, compose, identity

Constructor Detail

JELFunction

public JELFunction(String xvarname,
                   String fexpr)
            throws gnu.jel.CompilationException

Constructs a function with no external constants.

Parameters:

xvarname - name of the independent variable (for instance "x")

fexpr - text of expression giving the function value, in terms of xvarname (for instance "x+1")

Throws:

gnu.jel.CompilationException

JELFunction

public JELFunction(String xvarname,
                   String fexpr,
                   Map<String,? extends Constant<?>> constMap)
            throws gnu.jel.CompilationException

Constructs a function that can reference provided constants.

Parameters:

xvarname - name of the independent variable (for instance "x")

fexpr - text of expression giving the function value, in terms of xvarname (for instance "x+1")

constMap - map by name of constant values that can be referenced in the expression, may be null

Throws:

gnu.jel.CompilationException

Method Detail

getReferencedConstants

public Constant<?>[] getReferencedConstants()

Returns an array of any constants that were referenced in this function's expression. This list does not include an entry for the X value expression.

Returns:

constants from the map supplied at construction time that are referenced in this function's expression

evaluate

public double evaluate(double x)

Evaluates this function at a given value of the independent variable. In case of an evaluation error of some kind, NaN is returned.

Parameters:

x - variable value

Returns:

function value

applyAsDouble

public double applyAsDouble(double x)

Does exactly the same as evaluate(double).

Specified by:

applyAsDouble in interface java.util.function.DoubleUnaryOperator

getXVarName

public String getXVarName()

Returns the name of the independent variable.

Returns:

x variable name

getExpression

public String getExpression()

Returns the text of the function expression.

Returns:

function expression

main

public static void main(String[] args)

Main method tests this class. Args are varname, expr, varvalue, for instance "x", "3x+1", "29"