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multifit.C File Reference

## Detailed Description

Fitting multiple functions to different ranges of a 1-D histogram Example showing how to fit in a sub-range of an histogram A histogram is created and filled with the bin contents and errors defined in the table below.

Three 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.

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Chi2 = 0.0848003
NDf = 7
Edm = 8.86911e-08
NCalls = 106
Constant = 4.96664 +/- 2.83221
Mean = 95.4663 +/- 12.3905
Sigma = 6.82779 +/- 7.49131 (limited)
****************************************
Chi2 = 0.0771026
NDf = 7
Edm = 1.00182e-07
NCalls = 73
Constant = 5.96312 +/- 1.14355
Mean = 100.467 +/- 1.53372
Sigma = 3.54806 +/- 1.16899 (limited)
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Chi2 = 0.00877492
NDf = 8
Edm = 4.98832e-06
NCalls = 87
Constant = 0.912053 +/- 0.435309
Mean = 116.304 +/- 8.32344
Sigma = 8.38103 +/- 18.5139 (limited)
****************************************
Chi2 = 0.31282
NDf = 31
Edm = 3.25006e-06
NCalls = 495
p0 = 4.91052 +/- 1.41324
p1 = 94.4492 +/- 3.71244
p2 = 5.9461 +/- 2.41662
p3 = 3.22456 +/- 3.11384
p4 = 101.662 +/- 1.67862
p5 = 2.48631 +/- 1.91151
p6 = 0.911626 +/- 0.368736
p7 = 117.581 +/- 5.06092
p8 = 7.59194 +/- 8.78217
#include "TH1.h"
#include "TF1.h"
void multifit()
{
const int np = 49;
float 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};
// The histogram are filled with bins defined in the array x.
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]);
}
// Define the parameter array for the total function.
double par[9];
// Three TF1 objects are created, one for each subrange.
TF1 *g1 = new TF1("g1", "gaus", 85, 95);
TF1 *g2 = new TF1("g2", "gaus", 98, 108);
TF1 *g3 = new TF1("g3", "gaus", 110, 121);
// The total is the sum of the three, each has three parameters.
TF1 *total = new TF1("total", "gaus(0)+gaus(3)+gaus(6)", 85, 125);
total->SetLineColor(2);
// Fit each function and add it to the list of functions. By default,
// TH1::Fit() fits the function on the defined histogram range. You can
// specify the "R" option in the second parameter of TH1::Fit() to restrict
// the fit to the range specified in the TF1 constructor. Alternatively, you
// can also specify the range in the call to TH1::Fit(), which we demonstrate
// here with the 3rd Gaussian. The "+" option needs to be added to the later
// fits to not replace existing fitted functions in the histogram.
h->Fit(g1, "R");
h->Fit(g2, "R+");
h->Fit(g3, "+", "", 110, 121);
// Get the parameters from the fit.
g1->GetParameters(&par[0]);
g2->GetParameters(&par[3]);
g3->GetParameters(&par[6]);
// Use the parameters on the sum.
total->SetParameters(par);
h->Fit(total, "R+");
}
#define h(i)
Definition RSha256.hxx:106
static unsigned int total
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void char Point_t Rectangle_t WindowAttributes_t Float_t Float_t Float_t Int_t Int_t UInt_t UInt_t Rectangle_t Int_t Int_t Window_t TString Int_t GCValues_t GetPrimarySelectionOwner GetDisplay GetScreen GetColormap GetNativeEvent const char const char dpyName wid window const char font_name cursor keysym reg const char only_if_exist regb h Point_t np
1-Dim function class
Definition TF1.h:214
virtual Double_t * GetParameters() const
Definition TF1.h:526
1-D histogram with a float per channel (see TH1 documentation)}
Definition TH1.h:577
Double_t x[n]
Definition legend1.C:17

Definition in file multifit.C.