ExpSqrtPolyLDF.h

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#ifndef _LDFFinderKG_ExpSqrtPolyLDF_h_
#define _LDFFinderKG_ExpSqrtPolyLDF_h_


#include "VLDF.h"
#include <cmath>
#include <vector>
#include <utl/Math.h>
#include <utl/AugerUnits.h>


namespace LDFFinderKG {

  class ExpSqrtPolyLDF : public VLDF {

  public:
    ExpSqrtPolyLDF(const double refDistance) : VLDF(refDistance, 0, 2) { }

    double
    Value(const double r, const std::vector<double>& shape)
      const
    {
      const double z = std::sqrt(r);
      const double zRef = std::sqrt(fReferenceDistance);
      const double alpha = shape[0];
      const double beta  = shape[1];
      const double gamma = shape[2];
      const double delta = shape[3];

      // z0 is to make f(rRef) = 1
      const double z0 = -zRef*(alpha + zRef*(beta + zRef*(gamma + zRef*delta)));
      return std::exp(z0 + z*(alpha + z*(beta + z*(gamma + z*delta))));
    }

    double
    SecondDerivative(const double r, const std::vector<double>& shape)
      const
    {
      const double z = std::sqrt(r);
      const double alpha = shape[0];
      const double beta  = shape[1];
      const double gamma = shape[2];
      const double delta = shape[3];

      const double f = Value(r, shape);
      const double g = z*(0.5*alpha + z*(beta + z*(1.5*gamma + z*2*delta))) / r;
      const double dfdr = f * g;
      const double dgdr = z*(-0.25*alpha + z*z*(0.75*gamma + z*2*delta)) / (r*r);
      return dfdr*g + f*dgdr;
    }

    std::vector<double>
    ShapeModel(const double /* cosTheta */, const double /* showerSize */)
      const
    {
      // not implemented yet
      return std::vector<double>(4);
    }

    double
    BetaUncertainty(const double /* showerSize */)
      const
    {
      // not implemented yet
      return 0;
    }

    unsigned int GetNShapeParameters() const { return 4; }

  };

}


#endif