HcalChebyshevFunctor.cc

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#include "FWCore/Utilities/interface/Exception.h"

#include "CondFormats/HcalObjects/interface/HcalChebyshevFunctor.h"

HcalChebyshevFunctor::HcalChebyshevFunctor()
    : xmin_(-1.0), xmax_(1.0), outOfRangeValue_(0.0)
{
}

HcalChebyshevFunctor::HcalChebyshevFunctor(
    const std::vector<double>& coeffs,
    const double xmin, const double xmax,
    const double outOfRangeValue)
    : coeffs_(coeffs),
      xmin_(xmin),
      xmax_(xmax),
      outOfRangeValue_(outOfRangeValue)
{
    if (xmin_ >= xmax_) throw cms::Exception(
        "In HcalChebyshevFunctor constructor: invalid interval specification");
}

double HcalChebyshevFunctor::operator()(const double y) const
{
    if (!(y >= xmin_ && y <= xmax_))
        return outOfRangeValue_;

    if (coeffs_.empty())
        return 0.0;

    const double x = 2.0*(y - xmin_)/(xmax_ - xmin_) - 1.0;
    const double* a = &coeffs_[0];
    const double twox = 2.0*x;

    // Clenshaw recursion
    double rp2 = 0.0, rp1 = 0.0, r = 0.0;
    for (unsigned k = coeffs_.size()-1; k > 0U; --k)
    {
        r = twox*rp1 - rp2 + a[k];
        rp2 = rp1;
        rp1 = r;
    }
    return x*rp1 - rp2 + a[0];
}

BOOST_CLASS_EXPORT_IMPLEMENT(HcalChebyshevFunctor)