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--- software:analysis [2020/08/31 08:33] – himuser
+++ software:analysis [2022/01/14 18:44] (current) – external edit 127.0.0.1
@@ Line 4: / Line 4: @@
 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;
+  }