PLMD::SwitchingFunction Class Reference

Small class to compure switching functions. More...

#include <SwitchingFunction.h>

Public Member Functions
	SwitchingFunction ()
	Constructor. More...
void	set (int nn, int mm, double r_0, double d_0)
	Set a "rational" switching function. More...
void	set (const std::string &definition, std::string &errormsg)
	Set an arbitrary switching function. More...
std::string	description () const
	Returns a string with a description of the switching function. More...
double	calculate (double x, double &df) const
	Compute the switching function. More...
double	calculateSqr (double distance2, double &dfunc) const
	Compute the switching function. More...
double	inverse (const double &val) const
	Calculate the x value for a given y value. More...
double	get_d0 () const
	Returns d0. More...
double	get_r0 () const
	Returns r0. More...

Static Public Member Functions
static void	registerKeywords (Keywords &keys)

Private Types
enum	{ rational, exponential, gaussian, smap }
	Type of function. More...

Private Member Functions
double	do_rational (double rdist, double &dfunc, int nn, int mm) const
	Low-level tool to compute rational functions. More...

Private Attributes
bool	init
	This is to check that switching function has been initialized. More...
enum PLMD::SwitchingFunction:: { ... }	type
	Type of function. More...
double	invr0
	Inverse of scaling length. More...
double	d0
	Minimum distance (before this, function is one) More...
double	dmax
	Maximum distance (after this, function is zero) More...
int	nn
	Exponents for rational function. More...
int	mm
int	a
	Parameters for smap function. More...
int	b
double	c
double	d
double	invr0_2
	Square of invr0, useful in calculateSqr() More...
double	dmax_2
	Square of dmax, useful in calculateSqr() More...
double	stretch
	Parameters for stretching the function to zero at d_max. More...
double	shift

Detailed Description

Small class to compure switching functions.

Switching functions are created using set() and then can be used with function calculate() or calculateSqr(). Since this is typically computed on a distance vector, the second all (calculateSqr()) allows to skip the calculation of a square root in some case, thus potentially increasing performances.

Member Enumeration Documentation

anonymous enum

private

Type of function.

Enumerator
rational
exponential
gaussian
smap

Constructor & Destructor Documentation

PLMD::SwitchingFunction::SwitchingFunction

(

)

Constructor.

Member Function Documentation

double PLMD::SwitchingFunction::calculate	(	double	x,
		double &	df
	)		const

Compute the switching function.

Returns s(x). df will be set to the value of the derivative of the switching function _divided_by_x

double PLMD::SwitchingFunction::calculateSqr	(	double	distance2,
		double &	dfunc
	)		const

Compute the switching function.

Returns \( s(\sqrt{x})\) . df will be set to the \( \frac{1}{\sqrt{x}}\frac{ds}{d\sqrt{x}}= 2 \frac{ds}{dx}\) (same as calculate()). The advantage is that in some case the expensive square root can be avoided (namely for rational functions, if nn and mm are even and d0 is zero)

std::string PLMD::SwitchingFunction::description

(

)

const

Returns a string with a description of the switching function.

double PLMD::SwitchingFunction::do_rational ( double  rdist, double &  dfunc, int  nn, int  mm  ) const

private

Low-level tool to compute rational functions.

It is separated since it is called both by calculate() and calculateSqr()

double PLMD::SwitchingFunction::get_d0

(

)

const

Returns d0.

double PLMD::SwitchingFunction::get_r0

(

)

const

Returns r0.

double PLMD::SwitchingFunction::inverse

(

const double &

val

)

const

Calculate the x value for a given y value.

void PLMD::SwitchingFunction::registerKeywords ( Keywords &  keys )

static

void PLMD::SwitchingFunction::set	(	int	nn,
		int	mm,
		double	r_0,
		double	d_0
	)

Set a "rational" switching function.

Notice that a d_max is set automatically to a value such that f(d_max)=0.00001.

void PLMD::SwitchingFunction::set	(	const std::string &	definition,
		std::string &	errormsg
	)

Set an arbitrary switching function.

Parse the string in definition and possibly returns errors in the errormsg string

Member Data Documentation

int PLMD::SwitchingFunction::a

private

Parameters for smap function.

int PLMD::SwitchingFunction::b

private

double PLMD::SwitchingFunction::c

private

double PLMD::SwitchingFunction::d

private

double PLMD::SwitchingFunction::d0

private

Minimum distance (before this, function is one)

double PLMD::SwitchingFunction::dmax

private

Maximum distance (after this, function is zero)

double PLMD::SwitchingFunction::dmax_2

private

Square of dmax, useful in calculateSqr()

bool PLMD::SwitchingFunction::init

private

This is to check that switching function has been initialized.

double PLMD::SwitchingFunction::invr0

private

Inverse of scaling length.

We store the inverse to avoid a division

double PLMD::SwitchingFunction::invr0_2

private

Square of invr0, useful in calculateSqr()

int PLMD::SwitchingFunction::mm

private

int PLMD::SwitchingFunction::nn

private

Exponents for rational function.

double PLMD::SwitchingFunction::shift

private

double PLMD::SwitchingFunction::stretch

private

Parameters for stretching the function to zero at d_max.

enum { ... } PLMD::SwitchingFunction::type

Type of function.

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

• tools/SwitchingFunction.h
• tools/SwitchingFunction.cpp