User class for performing function integration.

It will use the Gauss-Legendre Method for function integration in a given interval. This class is implemented from TF1::Integral().

Definition at line 37 of file GaussLegendreIntegrator.h.

Public Member Functions
	GaussLegendreIntegrator (int num=10, double eps=1e-12)
	Basic constructor of GaussLegendreIntegrator.

	~GaussLegendreIntegrator () override
	Default Destructor.

int	GetNumberPoints () const

void	GetWeightVectors (double x, double w) const
	Returns the arrays x and w containing the abscissa and weight of the Gauss-Legendre n-point quadrature formula.

int	NEval () const override
	return number of function evaluations in calculating the integral This is equivalent to the number of points

ROOT::Math::IntegratorOneDimOptions	Options () const override
	get the option used for the integration

void	SetAbsTolerance (double) override
	This method is not implemented.

void	SetNumberPoints (int num)
	Set the number of points used in the calculation of the integral.

void	SetOptions (const ROOT::Math::IntegratorOneDimOptions &opt) override
	set the options (should be re-implemented by derived classes -if more options than tolerance exist

void	SetRelTolerance (double) override
	Set the desired relative Error.

Public Member Functions inherited from ROOT::Math::GaussIntegrator
	GaussIntegrator (double absTol=-1, double relTol=-1)
	Default Constructor.

	~GaussIntegrator () override
	Destructor.

void	AbsValue (bool flag)
	Static function: set the fgAbsValue flag.

double	Error () const override
	Return the estimate of the absolute Error of the last Integral calculation.

double	Integral () override
	Returns Integral of function on an infinite interval.

double	Integral (const std::vector< double > &pts) override
	This method is not implemented.

double	Integral (double a, double b) override
	Returns Integral of function between a and b.

double	IntegralCauchy (double a, double b, double c) override
	This method is not implemented.

double	IntegralLow (double b) override
	Returns Integral of function on a lower semi-infinite interval.

double	IntegralUp (double a) override
	Returns Integral of function on an upper semi-infinite interval.

double	Result () const override
	Returns the result of the last Integral calculation.

void	SetFunction (const IGenFunction &) override
	Set integration function (flag control if function must be copied inside).

int	Status () const override
	return the status of the last integration - 0 in case of success

Public Member Functions inherited from ROOT::Math::VirtualIntegratorOneDim
	~VirtualIntegratorOneDim () override
	destructor: no operation

virtual ROOT::Math::IntegrationOneDim::Type	Type () const
	return type of integrator

Public Member Functions inherited from ROOT::Math::VirtualIntegrator
virtual	~VirtualIntegrator ()
	destructor: no operation

Protected Attributes
int	fNum
	Number of points used in the estimation of the integral.

double *	fW
	Weights of the points used.

double *	fX
	Abscisa of the points used.

Protected Attributes inherited from ROOT::Math::GaussIntegrator
double	fEpsAbs
	Absolute error.

double	fEpsRel
	Relative error.

const IGenFunction *	fFunction
	Pointer to function used.

double	fLastError
	Error from the last estimation.

double	fLastResult
	Result from the last estimation.

bool	fUsedOnce
	Bool value to check if the function was at least called once.

Private Member Functions
void	CalcGaussLegendreSamplingPoints ()
	Type: unsafe but fast interface filling the arrays x and w (static method)

double	DoIntegral (double a, double b, const IGenFunction *func) override
	Integration surrogate method.

Additional Inherited Members
Static Protected Attributes inherited from ROOT::Math::GaussIntegrator
static bool	fgAbsValue = false
	AbsValue used for the calculation of the integral.

#include <Math/GaussLegendreIntegrator.h>

Inheritance diagram for ROOT::Math::GaussLegendreIntegrator:

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Constructor & Destructor Documentation

◆ GaussLegendreIntegrator()

ROOT::Math::GaussLegendreIntegrator::GaussLegendreIntegrator	(	int	num = `10`,
		double	eps = `1e-12`
	)

Basic constructor of GaussLegendreIntegrator.

@param num Number of desired points to calculate the integration. @param eps Desired relative error.

Definition at line 23 of file GaussLegendreIntegrator.cxx.

◆ ~GaussLegendreIntegrator()

ROOT::Math::GaussLegendreIntegrator::~GaussLegendreIntegrator ( )

override

Default Destructor.

Definition at line 34 of file GaussLegendreIntegrator.cxx.

Member Function Documentation

◆ CalcGaussLegendreSamplingPoints()

void ROOT::Math::GaussLegendreIntegrator::CalcGaussLegendreSamplingPoints ( )

private

Type: unsafe but fast interface filling the arrays x and w (static method)

Given the number of sampling points this routine fills the arrays x and w of length num, containing the abscissa and weight of the Gauss-Legendre n-point quadrature formula.

Gauss-Legendre: W(x)=1 -1<x<1 (j+1)P_{j+1} = (2j+1)xP_j-jP_{j-1}

num is the number of sampling points (>0) x and w are arrays of size num eps is the relative precision

If num<=0 or eps<=0 no action is done.

Reference: Numerical Recipes in C, Second Edition

Definition at line 98 of file GaussLegendreIntegrator.cxx.