Resolution.h

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//
//
// File: hitfit/Resolution.h
// Purpose: Calculate resolutions for a quantity.
// Created: Jul, 2000, sss, based on run 1 mass analysis code.
//
// This object will calculate resolutions for some quantity.
// We have three parameters:
//
//   C - constant term
//   R - resolution term
//   N - noise term
//
// Given a `momentum' p, we calculate the uncertainty in a quantity x as
//
//   sigma(x) = sqrt (C^2 p^2 + R^2 p + N^2)
//
// In addition, we have an `inverse' flag.  If that is set,
// we take the inverse of p before doing the above calculation
// (and for p, `sigma(p)' is regarded as actually sigma(1/p)).
//
// We encode the resolution parameters into a string, from which these
// objects get initialized.  The format is
//
//    [-]C[,R[,N]]
//
// If a leading minus sign is present, that turns on the invert flag.
// Omitted parameters are set to 0.
//
// CMSSW File      : interface/Resolution.h
// Original Author : Scott Stuart Snyder <snyder@bnl.gov> for D0
// Imported to CMSSW by Haryo Sumowidagdo <Suharyo.Sumowidagdo@cern.ch>
//
 
#ifndef HITFIT_RESOLUTION_H
#define HITFIT_RESOLUTION_H
 
#include <string>
#include <iosfwd>
#include "CLHEP/Random/Random.h"
 
namespace hitfit {
 
  class Resolution
  //
  // Purpose: Calculate resolutions for a quantity.
  //
  {
  public:
    // Initialize from a string S.  The format is as described above.
    Resolution(std::string s = "");
 
    Resolution(double C, double R, double m, double N, bool inverse = false);
 
    // Initialize to a constant resolution RES.  I.e., sigma() will
    // always return RES.  If INVERSE is true, set the inverse flag.
    Resolution(double res, bool inverse = false);
 
    // Return the setting of the inverse flag.
    bool inverse() const;
 
    double C() const;
 
    double R() const;
 
    double m() const;
 
    double N() const;
 
    // Return the uncertainty for a momentum P.
    double sigma(double p) const;
 
    // Given a value X, measured for an object with momentum P,
    // pick a new value from a Gaussian distribution
    // described by this resolution --- with mean X and width sigma(P).
    double pick(double x, double p, CLHEP::HepRandomEngine& engine) const;
 
    // Dump, for debugging.
    friend std::ostream& operator<<(std::ostream& s, const Resolution& r);
 
  private:
    // The resolution parameters.
 
    double _constant_sigma;
 
    double _resolution_sigma;
 
    double _resolution_exponent;
 
    double _noise_sigma;
 
    bool _inverse;
  };
 
}  // namespace hitfit
 
#endif  // not HITFIT_RESOLUTION_H