How to draw and fit the histogram

Newbie
1

Hii experts,

I have a dat file and want to fill a histogram. Ensure that each bin contains at least 5 counts.
Then after it will fit two Gaussian distributions. How to count at least 5 in each bin? kindly help me.
Here i have attached the macro:

TFile *f1 = new TFile(“count.root”, “RECREATE”);
TTree *tr = new TTree(“ntuple”, “data”);
tr->ReadFile(“hist_plot.dat”, “x”);
TH1F *h1 = new TH1F(“h1”, “Gaussian Distribution”, 20, -2.4, 2.9);
h1->GetXaxis()->SetTitle(“log_{10}(Value)”);
h1->GetYaxis()->SetTitle(“Counts (Frequency)”);
tr->Project(“h1”, “log10(x)”);
f1->Write();
TCanvas *c1 = new TCanvas();
c1->cd(1);
h1->Draw(“hist”);

Thanks,
Anil

2

Hi,
I would do something like this

bool check_bins=kTrue;
int i=1;
do{

if(h1->GetBinContent(i)<5)
check_bins=kFalse;
i++;
}while(check_bins  && i<=h1->GetNbinsX())

if checks_bin is true after the do-while loop all your bins have more than 5 counts

Stefano

1 Like
3

Thank you @Dilicus. The first two bins contain less than 5 counts however others are fine. Should we add these two bin counts so that it might be at least 5?

4

It is wrong to modify the data.
What you can do is to exclude the first bins from the fit or better you can do a fit using the sum of a gaussian for the signal and a pol(0) or pol(1) for the background

5

Ok will try. Thank you @Dilicus

6

I want to fit double Gaussian into a histogram. Here is the macro:

TFile *f = new TFile("assign1.root");
TH1F *h1 = (TH1F*)f->Get("h1");
TF1 *g1 = new TF1("fit1", "gaus", -2.4,1.);
g1->SetLineColor(kRed);
TF1 *g2 = new TF1("fit2", "gaus", 0., 2.9);
g2->SetLineColor(kGreen);
TF1 *f1 = new TF1("double_gaus", "gaus(0) + gaus(2)", -2.4, 2.9);
f1->SetParNames("Constant 1", "Mean 1", "Sigma 1", "Constant 2", "Mean 2", "Sigma 2");
f1->SetLineColor(kBlue);
gStyle->SetOptFit(1);
h1->Fit(g1, "R");
h1->Fit(g2, "R+");
Double_t par[6];
g1->GetParameters(&par[0]);
g2->GetParameters(&par[2]);
f1->SetParameters(par);
h1->Fit(f1, "R+");

I got the plot:

Screenshot from 2022-09-10 16-21-30
Screenshot from 2022-09-10 16-21-30703×544 8.29 KB

In the graph, the red line does not end at xaxis. I want fit the red line into small peak around -0.2 of the histogram. How do I do that. Kindly help me.

Thanks!
Anil

7

TF1 *f1 = new TF1("double_gaus", "gaus(0) + gaus(3)", -2.4, 2.9);

8

If I use "gaus(0) + gaus(3)". The blue line flats on xaxis and red does not change.
Screenshot from 2022-09-10 17-01-38

9

TF1 *g1 = new TF1("fit1", "gaus", -2.4, 0.1);
TF1 *g2 = new TF1("fit2", "gaus", 0.6, 2.9);
g2->GetParameters(&par[3]);

10

Here is the graph
Screenshot from 2022-09-10 20-25-37
But the end and start point of red and green lines respectively are not meet to xaxis. Can we meet them?

11

TF1 *g1 = new TF1("fit1", "gaus", -3., 3.); h1->Fit(g1, "", "", -2.4, 0.1);
TF1 *g2 = new TF1("fit2", "gaus", -3., 3.); h1->Fit(g2, "+", "", 0.6, 2.9);

h1->Fit(f1, "R+");
g1->SetParameters(f1->GetParameters()); g2->SetParameters(f1->GetParameters() + 3);
g1->Draw("SAME"); g2->Draw("SAME"); // f1->Draw("SAME");

12

Thank you very much @Wile_E_Coyote