How to write a TGraphErrors on a ROOT file?

ROOT
1

Hi all,
how to write a TGraphErrors on a ROOT file?
I write:

TFile *file = new TFile("file.root","RECREATE");
TGraphErrors *gr = new TGraphErrors(n,x,y,error_x,error_y);
file->Write();

but I have not result. Where is my error?
Thanks and best regards
Ciccio

2

Hi Ciccio,
see page 164 (Saving Objects to Disk) from ftp://root.cern.ch/root/doc/chapter11.pdf file->WriteTObject(gr);Jan

3

Hi Jan,
thank you for your answer.
Now I have a root_file with a graph, but this graph is empty.
If I write:

root [0] gr->Draw("AP")

I obtain the graph, but if I open the TBrowser and click on the “gr”, I obtain an empty canvas.
What I must do?
Best regards
Ciccio

P.S.: Sorry for my English

4

That’s weird. Do you have a small macro showing the problem ?

5

the macro is:

{
gROOT->Reset();
#include "Riostream.h"

Int_t n=3;

Int_t x[n]={1,2,3};
Int_t y[n]={1,2,3};

TFile *f = new TFile("file.root","RECREATE");

TGraph *gr1 = new TGraph(n,x,y);

gr1->SetMarkerStyle(7);
gr1->GetXaxis()->SetTitle("X");
gr1->GetYaxis()->SetTitle("Y");

f->WriteTObject(gr1);
}

but I have noticed that if I write:

root [0] gr->Draw()

I obtain the same risult: an empty canvas. Must I insert an option in “WriteTObject”?

6

It works perfectly for me. I ran:

{
 
        Int_t n=3;
 
        Int_t x[n]={1,2,3};
        Int_t y[n]={1,2,3};
 
        TFile *f = new TFile("file.root","RECREATE");
 
        TGraph *gr1 = new TGraph(n,x,y);
 
        gr1->SetMarkerStyle(7);
        gr1->GetXaxis()->SetTitle("X");
        gr1->GetYaxis()->SetTitle("Y");
        gr1->Draw("AC");
 
        f->WriteTObject(gr1);
}

it shows a graph. Then I exist ROOT and do:

root [0] TFile f("file.root");
root [1] Graph->Draw("AC")

and it displays the same graph.

7

Do you have the graph also from the TBrowser?

8

In the browser, in the “option” menu choice (top right) select “alp”.

9

YOU ARE BIG!!!

Thank you very much, now I view all graph.
Thank you
Ciccio