CrtCal.cc File Reference

#include "icaruscode/CRT/CRTDecoder/CrtCal.h"

Go to the source code of this file.

Macros
#define	CRT_CAL_CC

Functions
Double_t	langaufun (Double_t *x, Double_t *par)

Macro Definition Documentation

#define CRT_CAL_CC

Definition at line 2 of file CrtCal.cc.

Function Documentation

Double_t langaufun	(	Double_t *	x,
		Double_t *	par
	)

Definition at line 835 of file CrtCal.cc.

                                               {
 
    //Fit parameters:
    //par[0]=Width (scale) parameter of Landau density
    //par[1]=Most Probable (MP, location) parameter of Landau density
    //par[2]=Total area (integral -inf to inf, normalization constant)
    //par[3]=Width (sigma) of convoluted Gaussian function
    //
    //In the Landau distribution (represented by the CERNLIB approximation),
    //the maximum is located at x=-0.22278298 with the location parameter=0.
    //This shift is corrected within this function, so that the actual
    //maximum is identical to the MP parameter.
 
       // Numeric constants
       Double_t invsq2pi = 0.3989422804014;   // (2 pi)^(-1/2)
       Double_t mpshift  = -0.22278298;       // Landau maximum location
 
       // Control constants
       Double_t np = 100.0;      // number of convolution steps
       Double_t sc =   5.0;      // convolution extends to +-sc Gaussian sigmas
 
       // Variables
       Double_t xx;
       Double_t mpc;
       Double_t fland;
       Double_t sum = 0.0;
       Double_t xlow,xupp;
       Double_t step;
       Double_t i;
 
 
       // MP shift correction
       mpc = par[1] - mpshift * par[0];
 
       // Range of convolution integral
       xlow = x[0] - sc * par[3];
       xupp = x[0] + sc * par[3];
 
       step = (xupp-xlow) / np;
 
       // Convolution integral of Landau and Gaussian by sum
       for(i=1.0; i<=np/2; i++) {
          xx = xlow + (i-.5) * step;
          fland = TMath::Landau(xx,mpc,par[0]) / par[0];
          sum += fland * TMath::Gaus(x[0],xx,par[3]);
 
          xx = xupp - (i-.5) * step;
          fland = TMath::Landau(xx,mpc,par[0]) / par[0];
          sum += fland * TMath::Gaus(x[0],xx,par[3]);
       }
 
       return (par[2] * step * sum * invsq2pi / par[3]);
 }