FlightGear: JSBSim::FGFunction Class Reference

Represents a mathematical function. More...

#include <FGFunction.h>

Inherits JSBSim::FGParameter, and JSBSim::FGJSBBase.

Inherited by JSBSim::aFunc< func_t, 0 >, JSBSim::FGTemplateFunc, JSBSim::aFunc< func_t, Nmin >, and JSBSim::aFunc< func_t, 0 >.

Public Types
enum class	OddEven { Either , Odd , Even }

Public Types inherited from JSBSim::FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N. More...

enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R. More...

enum	{ eU = 1 , eV , eW }
	Velocities U, V, W. More...

enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z. More...

enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi. More...

enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift. More...

enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw. More...

enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down. More...

enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude. More...

enum	{ inNone = 0 , inDegrees , inRadians , inMeters , inFeet }
	Conversion specifiers. More...

Public Member Functions
	FGFunction ()
	Default constructor.

	FGFunction (FGPropertyManager *pm)

	FGFunction (FGFDMExec fdmex, Element element, const std::string &prefix="", FGPropertyValue *var=0L)
	Constructor.

	~FGFunction (void) override
	Destructor Make sure the function is untied before destruction.

double	GetValue (void) const override
	Retrieves the value of the function object.

std::string	GetValueAsString (void) const
	The value that the function evaluates to, as a string.

std::string	GetName (void) const override
	Retrieves the name of the function.

bool	IsConstant (void) const override
	Does the function always return the same result (i.e.

void	cacheValue (bool shouldCache)
	Specifies whether to cache the value of the function, so it is calculated only once per frame.

Public Member Functions inherited from JSBSim::FGParameter
virtual	~FGParameter (void)

double	getDoubleValue (void) const

Public Member Functions inherited from JSBSim::FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.

virtual	~FGJSBBase ()
	Destructor for FGJSBBase.

void	PutMessage (const Message &msg)
	Places a Message structure on the Message queue.

void	PutMessage (const std::string &text)
	Creates a message with the given text and places it on the queue.

void	PutMessage (const std::string &text, bool bVal)
	Creates a message with the given text and boolean value and places it on the queue.

void	PutMessage (const std::string &text, int iVal)
	Creates a message with the given text and integer value and places it on the queue.

void	PutMessage (const std::string &text, double dVal)
	Creates a message with the given text and double value and places it on the queue.

int	SomeMessages (void) const
	Reads the message on the queue (but does not delete it).

void	ProcessMessage (void)
	Reads the message on the queue and removes it from the queue.

Message *	ProcessNextMessage (void)
	Reads the next message on the queue and removes it from the queue.

void	disableHighLighting (void)
	Disables highlighting in the console output.

Protected Member Functions
void	Load (Element element, FGPropertyValue var, FGFDMExec *fdmex, const std::string &prefix="")

virtual void	bind (Element *, const std::string &)

void	CheckMinArguments (Element *el, unsigned int _min)

void	CheckMaxArguments (Element *el, unsigned int _max)

void	CheckOddOrEvenArguments (Element *el, OddEven odd_even)

std::string	CreateOutputNode (Element *el, const std::string &Prefix)

Protected Attributes
bool	cached

double	cachedValue

std::vector< FGParameter_ptr >	Parameters

FGPropertyManager *	PropertyManager

FGPropertyNode_ptr	pNode

Additional Inherited Members
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim.

static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit.

static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine.

static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius.

static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine.

static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin.

static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius.

static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit.

static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin.

static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius.

static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters.

static double	PitotTotalPressure (double mach, double p)
	Compute the total pressure in front of the Pitot tube.

static double	MachFromImpactPressure (double qc, double p)
	Compute the Mach number from the differential pressure (qc) and the static pressure.

static double	VcalibratedFromMach (double mach, double p)
	Calculate the calibrated airspeed from the Mach number.

static double	MachFromVcalibrated (double vcas, double p)
	Calculate the Mach number from the calibrated airspeed.Based on the formulas in the US Air Force Aircraft Performance Flight Testing Manual (AFFTC-TIH-99-01).

static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison.

static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison.

static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison.

static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison.

static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.

static constexpr double	sign (double num)

static double	GaussianRandomNumber (void)

Static Public Attributes inherited from JSBSim::FGJSBBase
static char	highint [5] = {27, '[', '1', 'm', '\0' }
	highlights text

static char	halfint [5] = {27, '[', '2', 'm', '\0' }
	low intensity text

static char	normint [6] = {27, '[', '2', '2', 'm', '\0' }
	normal intensity text

static char	reset [5] = {27, '[', '0', 'm', '\0' }
	resets text properties

static char	underon [5] = {27, '[', '4', 'm', '\0' }
	underlines text

static char	underoff [6] = {27, '[', '2', '4', 'm', '\0' }
	underline off

static char	fgblue [6] = {27, '[', '3', '4', 'm', '\0' }
	blue text

static char	fgcyan [6] = {27, '[', '3', '6', 'm', '\0' }
	cyan text

static char	fgred [6] = {27, '[', '3', '1', 'm', '\0' }
	red text

static char	fggreen [6] = {27, '[', '3', '2', 'm', '\0' }
	green text

static char	fgdef [6] = {27, '[', '3', '9', 'm', '\0' }
	default text

static short	debug_lvl = 1

static std::string	CreateIndexedPropertyName (const std::string &Property, int index)

static Message	localMsg

static std::queue< Message >	Messages

static unsigned int	messageId = 0

static constexpr double	radtodeg = 180. / 3.14159265358979323846

static constexpr double	degtorad = 3.14159265358979323846 / 180.

static constexpr double	hptoftlbssec = 550.0

static constexpr double	psftoinhg = 0.014138

static constexpr double	psftopa = 47.88

static constexpr double	ktstofps = 1.68781

static constexpr double	fpstokts = 1.0 / ktstofps

static constexpr double	inchtoft = 1.0/12.0

static constexpr double	fttom = 0.3048

static constexpr double	m3toft3 = 1.0/(fttomfttomfttom)

static constexpr double	in3tom3 = inchtoftinchtoftinchtoft/m3toft3

static constexpr double	inhgtopa = 3386.38

static constexpr double	slugtolb = 32.174049
	Note that definition of lbtoslug by the inverse of slugtolb and not to a different constant you can also get from some tables will make lbtoslug*slugtolb == 1 up to the magnitude of roundoff.

static constexpr double	lbtoslug = 1.0/slugtolb

static constexpr double	kgtolb = 2.20462

static constexpr double	kgtoslug = 0.06852168

static const std::string	needed_cfg_version = "2.0"

static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

static int	gaussian_random_number_phase = 0

Detailed Description

Represents a mathematical function.

The FGFunction class is a powerful and versatile resource that allows algebraic functions to be defined in a JSBSim configuration file. It is similar in concept to MathML (Mathematical Markup Language, www.w3.org/Math/), but simpler and more terse. A function definition consists of an operation, a value, a table, or a property (which evaluates to a value). The currently supported operations are:

sum (takes n args)
difference (takes n args)
product (takes n args)
quotient (takes 2 args)
pow (takes 2 args)
sqrt (takes one argument)
toradians (takes one argument)
todegrees (takes one argument)
exp (takes 2 args)
log2 (takes 1 arg)
ln (takes 1 arg)
log10 (takes 1 arg)
abs (takes 1 arg)
sin (takes 1 arg)
cos (takes 1 arg)
tan (takes 1 arg)
asin (takes 1 arg)
acos (takes 1 arg)
atan (takes 1 arg)
atan2 (takes 2 args)
min (takes n args)
max (takes n args)
avg (takes n args)
fraction
mod
floor (takes 1 arg)
ceil (takes 1 arg)
fmod (takes 2 args)
lt (less than, takes 2 args)
le (less equal, takes 2 args)
gt (greater than, takes 2 args)
ge (greater than, takes 2 args)
eq (equal, takes 2 args)
nq (not equal, takes 2 args)
and (takes n args)
or (takes n args)
not (takes 1 args)
if-then (takes 2-3 args)
switch (takes 2 or more args)
random (Gaussian distribution random number)
urandom (Uniform random number between -1 and +1)
pi
integer
interpolate 1-dimensional (takes a minimum of five arguments, odd number)

An operation is defined in the configuration file as in the following example:

<sum>
  <value> 3.14159 </value>
  <property> velocities/qbar </property>
  <product>
    <value> 0.125 </value>
    <property> metrics/wingarea </property>
  </product>
</sum>

A full function definition, such as is used in the aerodynamics section of a configuration file includes the function element, and other elements. It should be noted that there can be only one non-optional (non-documentation) element - that is, one operation element - in the top-level function definition. Multiple value and/or property elements cannot be immediate child members of the function element. Almost always, the first operation within the function element will be a product or sum. For example:

<function name="aero/moment/Clr">
    <description>Roll moment due to yaw rate</description>
    <product>
        <property>aero/qbar-area</property>
        <property>metrics/bw-ft</property>
        <property>aero/bi2vel</property>
        <property>velocities/r-aero-rad_sec</property>
        <table>
            <independentVar>aero/alpha-rad</independentVar>
            <tableData>
                 0.000  0.08
                 0.094  0.19
            </tableData>
        </table>
    </product>
</function>

The "lowest level" in a function is always a value or a property, which cannot itself contain another element. As shown, operations can contain values, properties, tables, or other operations. In the first above example, the sum element contains all three. What is evaluated is written algebraically as:

3.14159 + qbar + (0.125 * wingarea)

Some operations can take only a single argument. That argument, however, can be an operation (such as sum) which can contain other items. The point to keep in mind is that it evaluates to a single value - which is just what the trigonometric functions require (except atan2, which takes two arguments).

Specific Function Definitions

Note: In the definitions below, a "property" refers to a single property specified within either the <property></property> tag or the shortcut tag, . The keyword "value" refers to a single numeric value specified either within the <value></value> tag or the shortcut <v></v> tag. The keyword "table" refers to a single table specified either within the <table></table> tag or the shortcut <t></t> tag. The plural form of any of the three words refers to one or more instances of a property, value, or table.

sum, sums the values of all immediate child elements:
<sum>

{properties, values, tables, or other function elements}

</sum>

Example: Mach + 0.01

<sum>

 velocities/mach 

<v> 0.01 </v>

</sum>

p
#define p(x)
difference, subtracts the values of all immediate child elements from the value of the first child element:
<difference>

{properties, values, tables, or other function elements}

</difference>

Example: Mach - 0.01

<difference>

 velocities/mach 

<v> 0.01 </v>

</difference>
product multiplies together the values of all immediate child elements:
<product>

{properties, values, tables, or other function elements}

</product>

Example: qbar*S*beta*CY_beta

<product>

<property> aero/qbar-psf </property>

<property> metrics/Sw-sqft </property>

<property> aero/beta-rad </property>

<property> aero/coefficient/CY_beta </property>

</product>
quotient, divides the value of the first immediate child element by the second immediate child element:
<quotient>

{property, value, table, or other function element}

{property, value, table, or other function element}

</quotient>

Example: (2*GM)/R

<quotient>

<product>

<v> 2.0 </v>

 guidance/executive/gm 

</product>

 position/radius-to-vehicle-ft 

</quotient>

R
#define R
Definition metar_main.cxx:55
pow, raises the value of the first immediate child element to the power of the value of the second immediate child element:
<pow>

{property, value, table, or other function element}

{property, value, table, or other function element}

</pow>

Example: Mach^2

<pow>

 velocities/mach 

<v> 2.0 </v>

</pow>
sqrt, takes the square root of the value of the immediate child element:
<sqrt>

{property, value, table, or other function element}

</sqrt>

Example: square root of 25

<sqrt> <v> 25.0 </v> </sqrt>
toradians, converts a presumed argument in degrees to radians by multiplying the value of the immediate child element by pi/180:
<toradians>

{property, value, table, or other function element}

</toradians>

Example: convert 45 degrees to radians

<toradians> <v> 45 </v> </toradians>
todegrees, converts a presumed argument in radians to degrees by multiplying the value of the immediate child element by 180/pi:
<todegrees>

{property, value, table, or other function element}

</todegrees>

Example: convert 0.5*pi radians to degrees

<todegrees>

<product> <v> 0.5 </v> <pi/> </product>

</todegrees>

pi
static const double pi
Definition sview.cxx:59
exp, raises "e" to the power of the immediate child element:
<exp>

{property, value, table, or other function element}

</exp>

Example: raise "e" to the 1.5 power, e^1.5

<exp> <v> 1.5 </v> </exp>
log2, calculates the log base 2 value of the immediate child element:
<log2>

{property, value, table, or other function element}

</log2>

Example:

<log2> <v> 128 </v> </log2>
ln, calculates the natural logarithm of the value of the immediate child element:
<ln>

{property, value, table, or other function element}

</ln>

Example: ln(128)

<ln> <v> 200 </v> </ln>
log10, calculates the base 10 logarithm of the value of the immediate child element
<log10>

{property, value, table, or other function element}

</log10>

Example log(Mach)

<log10> velocities/mach </log10>
abs calculates the absolute value of the immediate child element
<abs>

{property, value, table, or other function element}

</abs>

Example:

<abs> flight-path/gamma-rad </abs>
sin, calculates the sine of the value of the immediate child element (the argument is expected to be in radians)
<sin>

{property, value, table, or other function element}

</sin>

Example:

<sin> <toradians> fcs/heading-true-degrees </toradians> </sin>
cos, calculates the cosine of the value of the immediate child element (the argument is expected to be in radians)
<cos>

{property, value, table, or other function element}

</cos>

Example:

<cos> <toradians> fcs/heading-true-degrees </toradians> </cos>
tan, calculates the tangent of the value of the immediate child element (the argument is expected to be in radians)
<tan>

{property, value, table, or other function element}

</tan>

Example:

<tan> <toradians> fcs/heading-true-degrees </toradians> </tan>
asin, calculates the arcsine (inverse sine) of the value of the immediate child element. The value provided should be in the range from -1 to +1. The value returned will be expressed in radians, and will be in the range from -pi/2 to +pi/2.
<asin>

{property, value, table, or other function element}

</asin>

Example:

<asin> <v> 0.5 </v> </asin>
acos, calculates the arccosine (inverse cosine) of the value of the immediate child element. The value provided should be in the range from -1 to +1. The value returned will be expressed in radians, and will be in the range from 0 to pi.
<acos>

{property, value, table, or other function element}

</acos>

Example:

<acos> <v> 0.5 </v> </acos>
atan, calculates the inverse tangent of the value of the immediate child element. The value returned will be expressed in radians, and will be in the range from -pi/2 to +pi/2.
<atan>

{property, value, table, or other function element}

</atan>

Example:

<atan> <v> 0.5 </v> </atan>
atan2 calculates the inverse tangent of the value of the immediate child elements, Y/X (in that order). It even works for X values near zero. The value returned will be expressed in radians, and in the range -pi to +pi.
<atan2>

{property, value, table, or other function element} {property, value, table, or other function element}

</atan2>

Example: inverse tangent of 0.5/0.25, evaluates to: 1.107 radians

<atan2> <v> 0.5 </<v> <v> 0.25 </v> </atan2>
min returns the smallest value from all the immediate child elements
<min>

{properties, values, tables, or other function elements}

</min>

Example: returns the lesser of velocity and 2500

<min>

 velocities/eci-velocity-mag-fps 

<v> 2500.0 </v>

</min>

min
#define min(X, Y)
Definition FGOutputFG.cpp:60
max returns the largest value from all the immediate child elements
<max>

{properties, values, tables, or other function elements}

</max>

Example: returns the greater of velocity and 15000

<max>

 velocities/eci-velocity-mag-fps 

<v> 15000.0 </v>

</max>
avg returns the average value of all the immediate child elements
<avg>

{properties, values, tables, or other function elements}

</avg>

Example: returns the average of the four numbers below, evaluates to 0.50.

<avg>

<v> 0.25 </v>

<v> 0.50 </v>

<v> 0.75 </v>

<v> 0.50 </v>

</avg>
fraction, returns the fractional part of the value of the immediate child element
<fraction>

{property, value, table, or other function element}

</fraction>

Example: returns the fractional part of pi - or, roughly, 0.1415926...

<fraction> <pi/> </fraction>
integer, returns the integer portion of the value of the immediate child element
<integer>

{property, value, table, or other function element}

</integer>
mod returns the remainder from the integer division of the value of the first immediate child element by the second immediate child element, X/Y (X modulo Y). The value returned is the value X-I*Y, for the largest integer I such that if Y is nonzero, the result has the same sign as X and magnitude less than the magnitude of Y. For instance, the expression "5 mod 2" would evaluate to 1 because 5 divided by 2 leaves a quotient of 2 and a remainder of 1, while "9 mod 3" would evaluate to 0 because the division of 9 by 3 has a quotient of 3 and leaves a remainder of 0.
<mod>

{property, value, table, or other function element}

{property, value, table, or other function element}

</mod>

Example: 5 mod 2, evaluates to 1

<mod> <v> 5 </v> <v> 2 </v> </mod>
floor returns the largest integral value that is not greater than X.
<floor>

{property, value, table, or other function element}

</floor>

Examples: floor(2.3) evaluates to 2.0 while floor(-2.3) evaluates to -3.0
ceil returns the smallest integral value that is not less than X.
<ceil>

{property, value, table, or other function element}

</ceil>

Examples: ceil(2.3) evaluates to 3.0 while ceil(-2.3) evaluates to -2.0
fmod returns the floating-point remainder of X/Y (rounded towards zero)
<fmod>

{property, value, table, or other function element}

{property, value, table, or other function element}

</fmod>

Example: fmod(18.5, 4.2) evaluates to 1.7
lt returns a 1 if the value of the first immediate child element is less than the value of the second immediate child element, returns 0 otherwise
<lt>

{property, value, table, or other function element}

{property, value, table, or other function element}

</lt>

Example: returns 1 if thrust is less than 10,000, returns 0 otherwise

<lt>

 propulsion/engine[2]/thrust-lbs 

<v> 10000.0 </v>

</lt>
le, returns a 1 if the value of the first immediate child element is less than or equal to the value of the second immediate child element, returns 0 otherwise
<le>

{property, value, table, or other function element}

{property, value, table, or other function element}

</le>

Example: returns 1 if thrust is less than or equal to 10,000, returns 0 otherwise

<le>

 propulsion/engine[2]/thrust-lbs 

<v> 10000.0 </v>

</le>
gt returns a 1 if the value of the first immediate child element is greater than the value of the second immediate child element, returns 0 otherwise
<gt>

{property, value, table, or other function element}

{property, value, table, or other function element}

</gt>

Example: returns 1 if thrust is greater than 10,000, returns 0 otherwise

<gt>

 propulsion/engine[2]/thrust-lbs 

<v> 10000.0 </v>

</gt>
ge, returns a 1 if the value of the first immediate child element is greater than or equal to the value of the second immediate child element, returns 0 otherwise
<ge>

{property, value, table, or other function element}

{property, value, table, or other function element}

</ge>

Example: returns 1 if thrust is greater than or equal to 10,000, returns 0

otherwise

<ge>

 propulsion/engine[2]/thrust-lbs 

<v> 10000.0 </v>

</ge>
eq returns a 1 if the value of the first immediate child element is equal to the second immediate child element, returns 0 otherwise
<eq>

{property, value, table, or other function element}

{property, value, table, or other function element}

</eq>

Example: returns 1 if thrust is equal to 10,000, returns 0 otherwise

<eq>

 propulsion/engine[2]/thrust-lbs 

<v> 10000.0 </v>

</eq>
nq returns a 1 if the value of the first immediate child element is not equal to the value of the second immediate child element, returns 0 otherwise
<nq>

{property, value, table, or other function element}

{property, value, table, or other function element}

</nq>

Example: returns 1 if thrust is not 0, returns 0 otherwise

<nq>

 propulsion/engine[2]/thrust-lbs 

<v> 0.0 </v>

</nq>
and returns a 1 if the values of the immediate child elements are all 1, returns 0 otherwise. Values provided are expected to be either 1 or 0 within machine precision.
<and>

{properties, values, tables, or other function elements}

</and>

Example: returns 1 if the specified flags are all 1

<and>

 guidance/first-stage-flight-flag 

 control/engines-running-flag 

</and>
or returns a 1 if the values of any of the immediate child elements 1, returns 0 otherwise. Values provided are expected to be either 1 or 0 within machine precision.
<or>

{properties, values, tables, or other function elements}

</or>

Example: returns 1 if any of the specified flags are 1

<or>

 guidance/first-stage-flight-flag 

 control/engines-running-flag 

</or>
not, returns the inverse of the value of the supplied immediate child element (e.g., returns 1 if supplied a 0)
<not>

{property, value, table, or other function element}

</not>

Example: returns 0 if the value of the supplied flag is 1

<not> guidance/first-stage-flight-flag </not>
ifthen if the value of the first immediate child element is 1, then the value of the second immediate child element is returned, otherwise the value of the third child element is returned
<ifthen>

{property, value, table, or other function element}

{property, value, table, or other function element}

{property, value, table, or other function element}

</ifthen>

Example: if flight-mode is greater than 2, then a value of 0.00 is

returned, otherwise the value of the property control/pitch-lag is

returned.

<ifthen>

<gt> executive/flight-mode <v> 2 </v> </gt>

<v> 0.00 </v>

 control/pitch-lag 

</ifthen>
switch uses the integer value of the first immediate child element as an index to select one of the subsequent immediate child elements to return the value of
<switch>

{property, value, table, or other function element}

{property, value, table, or other function element}

{property, value, table, or other function element}

...

</switch>

Example: if flight-mode is 2, the switch function returns 0.50

<switch>

 executive/flight-mode 

<v> 0.25 </v>

<v> 0.50 </v>

<v> 0.75 </v>

<v> 1.00 </v>

</switch>
random Returns a normal distributed random number. The function, without parameters, returns a normal distributed random value with a distribution defined by the parameters mean = 0.0 and standard deviation (stddev) = 1.0 The Mean of the distribution (its expected value, μ). Which coincides with the location of its peak. Standard deviation (σ): The square root of variance, representing the dispersion of values from the distribution mean. This shall be a positive value (σ>0).
<random/>

<random seed="1234"/>

<random seed="time_now"/>

<random seed="time_now" mean="0.0" stddev="1.0"/>

seed
static mt seed
Definition fgclouds.cxx:49
urandom Returns a uniformly distributed random number. The function, without parameters, returns a random value between the minimum value -1.0 and the maximum value of 1.0 The two maximum and minimum values can be modified using the lower and upper parameters.
<urandom/>

<random seed="1234"/>

<random seed="time_now"/>

<random seed="time_now" lower="-1.0" upper="1.0"/>
pi Takes no argument and returns the value of Pi
<pi/>
interpolate1d returns the result from a 1-dimensional interpolation of the supplied values, with the value of the first immediate child element representing the lookup value into the table, and the following pairs of values representing the independent and dependent values. The first provided child element is expected to be a property. The interpolation does not extrapolate, but holds the highest value if the provided lookup value goes outside of the provided range.
<interpolate1d>

{property, value, table, or other function element}

{property, value, table, or other function element} {property, value, table, or other function element}

...

</interpolate1d>

Example: If mach is 0.4, the interpolation will return 0.375. If mach is

1.5, the interpolation will return 0.60.

<interpolate1d>

 velocities/mach 

<v> 0.00 </v> <v> 0.25 </v>

<v> 0.80 </v> <v> 0.50 </v>

<v> 0.90 </v> <v> 0.60 </v>

</interpolate1d>

Author
Jon Berndt

Definition at line 752 of file FGFunction.h.

Member Enumeration Documentation

◆ OddEven

enum class JSBSim::FGFunction::OddEven

strong

Enumerator
Either
Odd
Even

Definition at line 814 of file FGFunction.h.

Constructor & Destructor Documentation

◆ FGFunction() [1/3]

JSBSim::FGFunction::FGFunction ( )

inline

Default constructor.

Definition at line 756 of file FGFunction.h.

◆ FGFunction() [2/3]

JSBSim::FGFunction::FGFunction ( FGPropertyManager * pm )

inlineexplicit

Definition at line 760 of file FGFunction.h.

◆ FGFunction() [3/3]

JSBSim::FGFunction::FGFunction	(	FGFDMExec *	fdmex,
		Element *	element,
		const std::string &	prefix = "",
		FGPropertyValue *	var = 0L )

Constructor.

When this constructor is called, the XML element pointed to in memory by the element argument is traversed. If other FGParameter-derived objects (values, functions, properties, or tables) are encountered, this instance of the FGFunction object will store a pointer to the found object and pass the relevant Element pointer to the constructor for the new object. In other words, each FGFunction object maintains a list of "child" FGParameter-derived objects which in turn may each contain its own list, and so on. At runtime, each object evaluates its child parameters, which each may have its own child parameters to evaluate.

Parameters

PropertyManager	a pointer to the property manager instance.
element	a pointer to the Element object containing the function definition.
prefix	an optional prefix to prepend to the name given to the property that represents this function (if given).

◆ ~FGFunction()

JSBSim::FGFunction::~FGFunction ( void )

override

Destructor Make sure the function is untied before destruction.

Definition at line 891 of file FGFunction.cpp.

Member Function Documentation

◆ bind()

void JSBSim::FGFunction::bind	(	Element *	,
		const std::string &	)

protectedvirtual

Definition at line 984 of file FGFunction.cpp.

◆ cacheValue()

void JSBSim::FGFunction::cacheValue ( bool shouldCache )

Specifies whether to cache the value of the function, so it is calculated only once per frame.

If shouldCache is true, then the value of the function is calculated, and a flag is set so further calculations done this frame will use the cached value. In order to turn off caching, cacheValue must be called with a false argument.

Parameters

shouldCache specifies whether the function should cache the computed value.

Definition at line 913 of file FGFunction.cpp.

◆ CheckMaxArguments()

void JSBSim::FGFunction::CheckMaxArguments	(	Element *	el,
		unsigned int	_max )

protected

Definition at line 255 of file FGFunction.cpp.

◆ CheckMinArguments()

void JSBSim::FGFunction::CheckMinArguments	(	Element *	el,
		unsigned int	_min )

protected

Definition at line 242 of file FGFunction.cpp.

◆ CheckOddOrEvenArguments()

void JSBSim::FGFunction::CheckOddOrEvenArguments	(	Element *	el,
		OddEven	odd_even )

protected

Definition at line 268 of file FGFunction.cpp.

◆ CreateOutputNode()

string JSBSim::FGFunction::CreateOutputNode	(	Element *	el,
		const std::string &	Prefix )

protected

Definition at line 948 of file FGFunction.cpp.

◆ GetName()

std::string JSBSim::FGFunction::GetName ( void ) const

inlineoverridevirtual

Retrieves the name of the function.

Implements JSBSim::FGParameter.

Definition at line 798 of file FGFunction.h.

◆ GetValue()

double JSBSim::FGFunction::GetValue ( void ) const

overridevirtual

Retrieves the value of the function object.

Returns: the total value of the function.

Implements JSBSim::FGParameter.

Definition at line 925 of file FGFunction.cpp.

◆ GetValueAsString()

string JSBSim::FGFunction::GetValueAsString ( void ) const

The value that the function evaluates to, as a string.

Returns: the value of the function as a string.

Definition at line 938 of file FGFunction.cpp.

◆ IsConstant()

bool JSBSim::FGFunction::IsConstant ( void ) const

overridevirtual

Does the function always return the same result (i.e.

does it apply to constant parameters) ?

Reimplemented from JSBSim::FGParameter.

Definition at line 901 of file FGFunction.cpp.

◆ Load()

void JSBSim::FGFunction::Load	(	Element *	element,
		FGPropertyValue *	var,
		FGFDMExec *	fdmex,
		const std::string &	prefix = "" )

protected

Definition at line 310 of file FGFunction.cpp.

Member Data Documentation

◆ cached

bool JSBSim::FGFunction::cached

protected

Definition at line 817 of file FGFunction.h.

◆ cachedValue

double JSBSim::FGFunction::cachedValue

protected

Definition at line 818 of file FGFunction.h.

◆ Parameters

std::vector<FGParameter_ptr> JSBSim::FGFunction::Parameters

protected

Definition at line 819 of file FGFunction.h.

◆ pNode

FGPropertyNode_ptr JSBSim::FGFunction::pNode

protected

Definition at line 821 of file FGFunction.h.

◆ PropertyManager

FGPropertyManager* JSBSim::FGFunction::PropertyManager

protected

Definition at line 820 of file FGFunction.h.

The documentation for this class was generated from the following files:

Public Types

Public Member Functions

Protected Member Functions

Protected Attributes

Additional Inherited Members

Detailed Description

Specific Function Definitions

Member Enumeration Documentation

◆ OddEven

Constructor & Destructor Documentation

◆ FGFunction() [1/3]

◆ FGFunction() [2/3]

◆ FGFunction() [3/3]

◆ ~FGFunction()

Member Function Documentation

◆ bind()

◆ cacheValue()

◆ CheckMaxArguments()

◆ CheckMinArguments()

◆ CheckOddOrEvenArguments()

◆ CreateOutputNode()

◆ GetName()

◆ GetValue()

◆ GetValueAsString()

◆ IsConstant()

◆ Load()

Member Data Documentation

◆ cached

◆ cachedValue

◆ Parameters

◆ pNode

◆ PropertyManager