RooPolynomial.cxx

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/*****************************************************************************
 * Project: RooFit                                                           *
 * Package: RooFitModels                                                     *
 * @(#)root/roofit:$Id$
 * Authors:                                                                  *
 *   WV, Wouter Verkerke, UC Santa Barbara, verkerke@slac.stanford.edu       *
 *   DK, David Kirkby,    UC Irvine,         dkirkby@uci.edu                 *
 *                                                                           *
 * Copyright (c) 2000-2005, Regents of the University of California          *
 *                          and Stanford University. All rights reserved.    *
 *                                                                           *
 * Redistribution and use in source and binary forms,                        *
 * with or without modification, are permitted according to the terms        *
 * listed in LICENSE (http://roofit.sourceforge.net/license.txt)             *
 *****************************************************************************/
 
/** \class RooPolynomial
    \ingroup Roofit
 
RooPolynomial implements a polynomial p.d.f of the form
\f[ f(x) = \mathcal{N} \cdot \sum_{i} a_{i} * x^i \f]
By default, the coefficient \f$ a_0 \f$ is chosen to be 1, as polynomial
probability density functions have one degree of freedom
less than polynomial functions due to the normalisation condition. \f$ \mathcal{N} \f$
is a normalisation constant that is automatically calculated when the polynomial is used
in computations.
 
The sum can be truncated at the low end. See the main constructor
RooPolynomial::RooPolynomial(const char*, const char*, RooAbsReal&, const RooArgList&, Int_t)
**/
 
#include "RooPolynomial.h"
#include "RooArgList.h"
#include "RooMsgService.h"
#include "RooPolyVar.h"
 
#include <RooFit/Detail/MathFuncs.h>
 
#include "TError.h"
#include <vector>
 
 
////////////////////////////////////////////////////////////////////////////////
/// Create a polynomial in the variable `x`.
/// \param[in] name Name of the PDF
/// \param[in] title Title for plotting the PDF
/// \param[in] x The variable of the polynomial
/// \param[in] coefList The coefficients \f$ a_i \f$
/// \param[in] lowestOrder [optional] Truncate the sum such that it skips the lower orders:
/// \f[
///     1. + \sum_{i=0}^{\mathrm{coefList.size()}} a_{i} * x^{(i + \mathrm{lowestOrder})}
/// \f]
///
/// This means that
/// \code{.cpp}
/// RooPolynomial pol("pol", "pol", x, RooArgList(a, b), lowestOrder = 2)
/// \endcode
/// computes
/// \f[
///   \mathrm{pol}(x) = 1 * x^0 + (0 * x^{\ldots}) + a * x^2 + b * x^3.
/// \f]
 
RooPolynomial::RooPolynomial(const char *name, const char *title, RooAbsReal &x, const RooArgList &coefList,
                             Int_t lowestOrder)
   : RooAbsPdf(name, title),
     _x("x", "Dependent", this, x),
     _coefList("coefList", "List of coefficients", this),
     _lowestOrder(lowestOrder)
{
   // Check lowest order
   if (_lowestOrder < 0) {
      coutE(InputArguments) << "RooPolynomial::ctor(" << GetName()
                            << ") WARNING: lowestOrder must be >=0, setting value to 0" << std::endl;
      _lowestOrder = 0;
   }
 
   _coefList.addTyped<RooAbsReal>(coefList);
}
 
////////////////////////////////////////////////////////////////////////////////
 
RooPolynomial::RooPolynomial(const char *name, const char *title, RooAbsReal &x)
   : RooAbsPdf(name, title),
     _x("x", "Dependent", this, x),
     _coefList("coefList", "List of coefficients", this)
{
}
 
////////////////////////////////////////////////////////////////////////////////
/// Copy constructor
 
RooPolynomial::RooPolynomial(const RooPolynomial &other, const char *name)
   : RooAbsPdf(other, name),
     _x("x", this, other._x),
     _coefList("coefList", this, other._coefList),
     _lowestOrder(other._lowestOrder)
{
}
 
////////////////////////////////////////////////////////////////////////////////
 
double RooPolynomial::evaluate() const
{
   const unsigned sz = _coefList.size();
   if (!sz)
      return _lowestOrder ? 1. : 0.;
 
   RooPolyVar::fillCoeffValues(_wksp, _coefList);
 
   return RooFit::Detail::MathFuncs::polynomial<true>(_wksp.data(), sz, _lowestOrder, _x);
}
 
/// Compute multiple values of Polynomial.
void RooPolynomial::doEval(RooFit::EvalContext &ctx) const
{
   return RooPolyVar::doEvalImpl(this, ctx, _x.arg(), _coefList, _lowestOrder);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Advertise to RooFit that this function can be analytically integrated.
Int_t RooPolynomial::getAnalyticalIntegral(RooArgSet &allVars, RooArgSet &analVars, const char * /*rangeName*/) const
{
   return matchArgs(allVars, analVars, _x);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Do the analytical integral according to the code that was returned by getAnalyticalIntegral().
double RooPolynomial::analyticalIntegral(Int_t code, const char *rangeName) const
{
   R__ASSERT(code == 1);
 
   const double xmin = _x.min(rangeName);
   const double xmax = _x.max(rangeName);
   const unsigned sz = _coefList.size();
   if (!sz)
      return _lowestOrder ? xmax - xmin : 0.0;
 
   RooPolyVar::fillCoeffValues(_wksp, _coefList);
 
   return RooFit::Detail::MathFuncs::polynomialIntegral<true>(_wksp.data(), sz, _lowestOrder, xmin, xmax);
}