What is nbinsx , xbins?

ROOT
1

Hi experts.
I was looking at the description of TH2F. And nbinsx and xbins came out, but i don’t know about this. What’s mean?

TH2F::TH2F ( const char * name,
const char * title,
Int_t nbinsx,
const Double_t * xbins,
Int_t nbinsy,
const Double_t * ybins
)

Also i wanna draw scatter plot. So how can i set the range?

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2

https://root.cern/doc/master/classTH1.html#a82f16fb9b9a11c97f1c9177e9e996fc7

3

How do you draw the scatter plot ? from a TTree ?
If that’s the case you can do:

your_tree->Draw("y:x")

In that case the range will be calculate automatically.
One way to fix the range will be:

auto h2 = new TH2F("h2","h2",........)
your_tree->Draw("y:x >> h2")
4

Thanks for reply!

My data comes from a ntp.

What is auto used for? And What is the role of ‘>>’?

5

Thanks for reply!

I’m the beginner of root. So It’s little hard to understand. nbins is number if bins in x axis? And i can’t understand what is xbins.

6
  • auto is C++ used to declare a variable automatically. here a TH2F
  • >> tells Draw to fill the histogram h2
TH2D::TH2D	(	const char * 	name, // Histogram name
                const char * 	title, // Histogram title
                Int_t 	nbinsx, // number of bins along X 
                const Double_t * 	xbins, // A Vector describing the bins along X - dimension is nbinsx+1
                Int_t 	nbinsy, // number of bins along Y
                const Double_t * 	ybins, // A Vector describing the bins along Y- dimension is nbinsy+1
)
7

Thanks for reply! It really helps me.

8

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