Polynomial.h

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// @(#)root/mathmore:$Id$
// Authors: L. Moneta, A. Zsenei   08/2005
 
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  * Copyright (c) 2004 ROOT Foundation,  CERN/PH-SFT                   *
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// Header file for class Polynomial
//
// Created by: Lorenzo Moneta  at Wed Nov 10 17:46:19 2004
//
// Last update: Wed Nov 10 17:46:19 2004
//
#ifndef ROOT_Math_Polynomial
#define ROOT_Math_Polynomial
 
#include <complex>
#include <vector>
 
#include "Math/ParamFunction.h"
 
// #ifdef _WIN32
// #pragma warning(disable : 4250)
// #endif
 
namespace ROOT {
namespace Math {
 
//_____________________________________________________________________________________
  /**
     Parametric Function class describing polynomials of order n.
 
     <em>P(x) = p[0] + p[1]*x + p[2]*x**2 + ....... + p[n]*x**n</em>
 
     The class implements also the derivatives, \a dP(x)/dx and the \a dP(x)/dp[i].
 
     The class provides also the method to find the roots of the polynomial.
     It uses analytical methods up to quartic polynomials.
 
     Implements both the Parameteric function interface and the gradient interface
     since it provides the analytical gradient with respect to x
 
 
     @ingroup ParamFunc
  */
 
class Polynomial : public ParamFunction<IParamGradFunction>,
                   public IGradientFunctionOneDim
{
 
 
public:
 
 typedef  ParamFunction<IParamGradFunction> ParFunc;
   /**
      Construct a Polynomial function of order n.
      The number of Parameters is n+1.
   */
 
   Polynomial(unsigned int n = 0);
 
   /**
      Construct a Polynomial of degree  1 : a*x + b
   */
   Polynomial(double a, double b);
 
   /**
      Construct a Polynomial of degree  2 : a*x**2 + b*x + c
   */
   Polynomial(double a, double b, double c);
 
   /**
      Construct a Polynomial of degree  3 : a*x**3 + b*x**2 + c*x + d
   */
   Polynomial(double a, double b, double c, double d);
 
   /**
      Construct a Polynomial of degree  4 : a*x**4 + b*x**3 + c*x**2 + dx  + e
   */
   Polynomial(double a, double b, double c, double d, double e);
 
 
   ~Polynomial() override {}
 
   // use default copy-ctor and assignment operators
 
 
 
//   using ParamFunction::operator();
 
   /**
      Find the polynomial roots.
      For n <= 4, the roots are found analytically while for larger order an iterative numerical method is used
      The numerical method used is from GSL (see <A HREF="https://www.gnu.org/software/gsl/doc/html/poly.html">documentation</A> )
      For the case of n = 4 by default an analytical algorithm is used from an implementation by
       Andrew W. Steiner and Andy Buckley which is a translation from the original Cenrlib routine
       (< HREF="https://cds.cern.ch/record/2050876/files/c208.html">RRTEQ4</A> ).
      Note that depending on the coefficients the result could be not very accurate if the discriminant of the resolvent cubic
      equation is very small. In that case it might be more robust to use the numerical method, by calling directly FindNumRoots()
 
   */
   std::vector<std::complex<double>> FindRoots() const;
 
   /**
      Find the only the real polynomial roots.
      For n <= 4, the roots are found analytically while for larger order an iterative numerical method is used
      The numerical method used is from GSL (see <A HREF="https://www.gnu.org/software/gsl/doc/html/poly.html">documentation</A> )
   */
   std::vector<double> FindRealRoots() const;
 
   /**
      Find the polynomial roots using always an iterative numerical methods
      The numerical method used is from GSL (see <A HREF="https://www.gnu.org/software/gsl/doc/html/poly.html">documentation</A> )
   */
   std::vector<std::complex<double>> FindNumRoots() const;
 
   /**
      Order of Polynomial
   */
   unsigned int Order() const { return fOrder; }
 
 
   IGenFunction * Clone() const override;
 
   /**
       Optimized method to evaluate at the same time the function value and derivative at a point x.
       Implement the interface specified by ROOT::Math::IGradientOneDim.
       In the case of polynomial there is no advantage to compute both at the same time
   */
   void FdF (double x, double & f, double & df) const override {
      f = (*this)(x);
      df = Derivative(x);
   }
 
 
private:
 
   double DoEvalPar ( double x, const double * p ) const override ;
 
   double DoDerivative (double x) const override ;
 
   double DoParameterDerivative(double x, const double * p, unsigned int ipar) const override;
 
 
   // cache order = number of params - 1)
   unsigned int fOrder;
 
   // cache Parameters for Gradient
   mutable std::vector<double> fDerived_params;
};
 
} // namespace Math
} // namespace ROOT
 
 
#endif /* ROOT_Math_Polynomial */