GaussLegendreIntegrator.h

Go to the documentation of this file.

// @(#)root/mathcore:$Id$
// Authors: David Gonzalez Maline    01/2008
 
/**********************************************************************
 *                                                                    *
 * Copyright (c) 2006 , LCG ROOT MathLib Team                         *
 *                                                                    *
 *                                                                    *
 **********************************************************************/
 
// Header file for GaussIntegrator
//
// Created by: David Gonzalez Maline  : Wed Jan 16 2008
//
 
#ifndef ROOT_Math_GaussLegendreIntegrator
#define ROOT_Math_GaussLegendreIntegrator
 
 
#include "Math/GaussIntegrator.h"
 
 
namespace ROOT {
namespace Math {
 
//___________________________________________________________________________________________
/**
   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().
 
   @ingroup Integration
 
 */
 
class GaussLegendreIntegrator: public GaussIntegrator {
public:
 
   /** Basic constructor of GaussLegendreIntegrator.
       \@param num Number of desired points to calculate the integration.
       \@param eps Desired relative error.
   */
   GaussLegendreIntegrator(int num = 10 ,double eps=1e-12);
 
   /** Default Destructor */
   ~GaussLegendreIntegrator() override;
 
   /** Set the number of points used in the calculation of the
       integral */
   void SetNumberPoints(int num);
 
   /** Set the desired relative Error. */
   void SetRelTolerance (double) override;
 
   /** This method is not implemented. */
   void SetAbsTolerance (double) override;
 
 
   /** Returns the arrays x and w 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}
   */
   void GetWeightVectors(double *x, double *w) const;
 
   int GetNumberPoints() const { return fNum; }
 
   /**
       return number of function evaluations in calculating the integral
       This is equivalent to the number of points
   */
   int NEval() const override { return fNum; }
 
 
   ///  get the option used for the integration
   ROOT::Math::IntegratorOneDimOptions Options() const override;
 
   // set the options
   void SetOptions(const ROOT::Math::IntegratorOneDimOptions & opt) override;
 
private:
 
   /**
      Integration surrogate method. Return integral of passed function in  interval [a,b]
      Reimplement method of GaussIntegrator using CalcGaussLegendreSamplingPoints
   */
   double DoIntegral (double a, double b, const IGenFunction* func) override;
 
   /**
      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
   */
   void CalcGaussLegendreSamplingPoints();
 
 
protected:
   int fNum;                 ///< Number of points used in the estimation of the integral.
   double* fX;               ///< Abscisa of the points used.
   double* fW;               ///< Weights of the points used.
 
};
 
} // end namespace Math
 
} // end namespace ROOT
 
#endif /* ROOT_Math_GaussLegendreIntegrator */