# Fitting MANY MANY multiple functions to different ranges of

Regarding Tutorial multifit.C: “Fitting multiple functions to different ranges of a 1-D histogram”…

/////////////////////////////////////////////////////////////////////////////////////////////////
#include “TH1.h”
#include “TF1.h”

void multifit() {
// Fitting multiple functions to different ranges of a 1-D histogram
// To see the output of this macro, click begin_html here end_html
// Example showing how to fit in a sub-range of an histogram
// An histogram is created and filled with the bin contents and errors
// defined in the table below.
// 3 gaussians are fitted in sub-ranges of this histogram.
// A new function (a sum of 3 gaussians) is fitted on another subrange
// Note that when fitting simple functions, such as gaussians, the initial
// values of parameters are automatically computed by ROOT.
// In the more complicated case of the sum of 3 gaussians, the initial values
// of parameters must be given. In this particular case, the initial values
// are taken from the result of the individual fits.
//Author: Rene Brun

const Int_t np = 49;
Float_t x[np] = {1.913521, 1.953769, 2.347435, 2.883654, 3.493567,
4.047560, 4.337210, 4.364347, 4.563004, 5.054247,
5.194183, 5.380521, 5.303213, 5.384578, 5.563983,
5.728500, 5.685752, 5.080029, 4.251809, 3.372246,
2.207432, 1.227541, 0.8597788,0.8220503,0.8046592,
0.7684097,0.7469761,0.8019787,0.8362375,0.8744895,
0.9143721,0.9462768,0.9285364,0.8954604,0.8410891,
0.7853871,0.7100883,0.6938808,0.7363682,0.7032954,
0.6029015,0.5600163,0.7477068,1.188785, 1.938228,
2.602717, 3.472962, 4.465014, 5.177035};

TH1F *h = new TH1F(“h”,“Example of several fits in subranges”,np,85,134);
h->SetMaximum(7);

for (int i=0;i<np;i++) {
h->SetBinContent(i+1,x[i]);
}

Double_t par[9];
TF1 *g1 = new TF1(“g1”,“gaus”,85,95);
TF1 *g2 = new TF1(“g2”,“gaus”,98,108);
TF1 *g3 = new TF1(“g3”,“gaus”,110,121);
TF1 *total = new TF1(“total”,“gaus(0)+gaus(3)+gaus(6)”,85,125);
total->SetLineColor(2);
h->Fit(g1,“R”);
h->Fit(g2,“R+”);
h->Fit(g3,“R+”);
g1->GetParameters(&par[0]);
g2->GetParameters(&par[3]);
g3->GetParameters(&par[6]);
total->SetParameters(par);
h->Fit(total,“R+”);
}
/////////////////////////////////////////////////////////////////////////////////////////////////

…at https://root.cern.ch/root/htmldoc/tutorials/fit/multifit.C.html …how might one modify this to cover an arbitrary number of gaussian functions, beyond 3 as here, please? That is, effectively write…

TF1 *g1 = new TF1(“g1”,“gaus”,85,95);
TF1 *g2 = new TF1(“g2”,“gaus”,98,108);
TF1 *g3 = new TF1(“g3”,“gaus”,110,121);

and

TF1 *total = new TF1(“total”,“gaus(0)+gaus(3)+gaus(6)”,85,125);

and

g1->GetParameters(&par[0]);
g2->GetParameters(&par[3]);
g3->GetParameters(&par[6]);

…in alternative – or the entire macro with a different(?) approach – manners so as to cover the arbitrary-number-of-gaus functions case of interest? Many, many thanks, guyrbennett

Hi,

You need modify the macro to create a list of functions. You are probably better using a C++ based TF1 instead of a TFormula based to build the total function

Best Regards

Lorenzo