Hi, ROOTers.
I am trying to fit scintillation curve with two exponents convolved with gaussian.
Here is my code
Fitting function
Part of interest is between #ifdef CONV and #endif directives.
#include <TFile.h>
#include <TTree.h>
#include <TH1F.h>
#include <TStyle.h>
#include <TF1.h>
#include <TAxis.h>
#include <TF1Convolution.h>
#include "Tau.h"
#define CONV
void FitWaveform()
{
TFile* file = TFile::Open( "../draw_waveforms/TotalWaveforms.root" );
TH1F* hist = (TH1F*)file->Get( "totalWaveform" );
const double x0 = 250;//start of fitting
const double xMax = hist->GetXaxis()->GetXmax();
const double xMin = hist->GetXaxis()->GetXmin();
const double length = xMax - xMin;
const double yMin = hist->GetMinimum();
TF1* twoExpos = new TF1( "twoExpos", TwoExponents, x0, xMax, 6 );
twoExpos->SetParameters( yMin*0.8,
0.1*length,
x0,
yMin*0.2,
0.5*length,
x0 );
twoExpos->SetParNames( "A1", "tau1", "x0", "A2", "tau2", "x0" );
twoExpos->SetParLimits( 1, 0, length);
twoExpos->SetParLimits( 4, 0, length );
twoExpos->SetParLimits( 2, x0, x0);
twoExpos->SetParLimits( 5, x0, x0);
TF1* gaus = new TF1( "gaus", "gaus", -10, 10 );
#ifdef CONV
TF1Convolution* expoGaus = new TF1Convolution( twoExpos, gaus, false );//FFTW not available
expoGaus->SetRange( x0, xMax );
TF1* fit = new TF1( "fit", *expoGaus, x0, xMax, expoGaus->GetNpar() );
fit->SetParameters( yMin*0.8,
0.1*length,
x0,
yMin*0.2,
0.5*length,
x0,
1.0,
0.,
1.0 );
fit->SetParLimits( 1, 0, length );
fit->SetParLimits( 4, 0, length );
fit->SetParLimits( 2, x0, x0);
fit->SetParLimits( 5, x0, x0);
fit->SetParLimits( 6, 1.0, 1.0 );
fit->SetParLimits( 7, 0., 0. );
fit->SetParLimits( 8, 1.0, 1.0 );
hist->Fit( fit, "R" );
#else
hist->Fit( twoExpos, "R" );
#endif
gStyle->SetOptFit(1111);
}
TwoExponents function
It’s just sum of two exponents. No surprise.
Here is the code.
#include <TMath.h>
double Exponent( double* x, double* par )
{
double A = par[0];
double tau = par[1];
double x0 = par[2];
double arg = 0.;
if( tau > 0. )
{
arg = -(x[0] - x0) / tau;
}
return A * TMath::Exp( arg );
}
double TwoExponents( double* x, double* par )
{
return Exponent( x, par ) + Exponent( x, &par[3] );
}
Problem
Fit fails. What am I doing wrong?
NOTES
Firstly, if I fit it with just two exponents it fits well.
sumOfWaveformsFit.pdf (53.8 KB)
Secondly, bin’s content of the histogram is DOUBLE numbers not INT.
Thirdly, here is the root file TotalWaveforms.root (18.4 KB)
ROOT Version: 6.15/01
Platform: Ubuntu 16.04