===== Analysis tools =====

===Novosibirsk function===

The Novosibirsk function is typically used to fit monoenergetic electromagnetic calorimeter spectra.
Explanations on this function are given here {{ :software:novosibirsk.pdf |}}.

A C++ code snippet to calculate the function using ROOT classes is given below. The interface is chosen to be usable with the ROOT fitting routines, e.g. ''TH1::Fit()''. It takes two arrays as input. From the first one only the first element is used as ''x'', From the second array, the values of the fit parameters are taken.

  #include "TMath.h" 
  
  /*   p[0] = normalisation constant   
       p[1] = peak position   
       p[2] = sigma (energy  resolution)   
       p[3] = eta (asymmetry parameter)   
       p[4] = constant background  
  */ 
  double novosibirsk(double *x, double *p) 
  {   
     double xi=2.35482004503094933e+00;
     double Y=(x[0]-p[1])*p[3]/p[2];
  
     if(Y>=1) return p[4];
  
     double lnX = log( 1. - Y );   
     double s0  = 2/xi*TMath::ASinH(p[3]*xi*0.5);   
     double s02 = s0*s0;   
    
     double f = p[0]*exp ( -0.5/s02 * lnX*lnX - 0.5*s02) + p[4];     
     return f; 
  }