TGraph, SetTitle, SetLog

ROOT
1

Hi there,

Strange bug…
xtitle disappears whilst requesting logx (in either interpreted or compiled mode).
It depends on the number of lines in misc.txt.
If one removes the last line (line #18), everything’s fine.
The problem arises from version 5.24/00.
No prob with version 5.22/00.

Cheers,
Z

#include <TGraph.h> #include <TCanvas.h> #include <TPad.h> #include <TAxis.h> void ztemp () { TGraph *graph = new TGraph ("misc.txt","%lg %lg") ; graph->GetXaxis()->SetTitle("foo") ; TCanvas* canvas = new TCanvas ("canvas") ; printf ("\nxtitle = '%s'\n", graph->GetXaxis()->GetTitle()) ; gPad->SetLogx() ; printf ("\nxtitle = '%s'\n", graph->GetXaxis()->GetTitle()) ; return ; }
misc.txt (450 Bytes)

2

Like that it is ok:

void ztemp ()
{
   TCanvas* canvas = new TCanvas ("canvas") ;
   canvas->SetLogx() ;
   TGraph *graph = new TGraph ("misc.txt","%lg %lg") ;
   graph->GetXaxis()->SetTitle("foo") ;
   graph->Draw("AL");
}

gPad exist only if Draw has been perform.

3

Thanks Olivier.
In that case, this is only the “canvas->SetLogx()” statement that makes it not to work (from 5.24).

TGraph *graph = new TGraph ("misc.txt","%lg %lg") ; graph->GetXaxis()->SetTitle("foo") ; //TFile *fout = new TFile ("ztemp.root","recreate") ; //graph->Write() ; TCanvas* canvas = new TCanvas ("canvas") ; //canvas->SetLogx() ; graph->Draw("al") ;I don’t like the idea of mixing the “output print/plot” part and the “input/create data” part.
The TGraph object and its properties should be independent of it (everything can be saved in a TFile without any plotting).
For sure, I’m missing something (no prob in the past) but isn’t there any other way to deal with this?
TIA,
Z

4

I don’t understand the bug yet. I just came with something even simpler than your example which reproduces the problem:

void ztemp ()
{
   TCanvas* canvas = new TCanvas ("canvas") ;
   TGraph *graph = new TGraph ();
   graph->SetPoint(0, 0.00100, 30.00);      
   graph->SetPoint(1, 0.00155, 20.00);      
// Uncomment the next line and the axis title disappear.
//   graph->SetPoint(2, 0.01250, 10.00);    

   graph->Draw("AL*");
   graph->GetXaxis()->SetTitle("foo") ;
   gPad->SetLogx() ;   
}

I am still investigating

5

Hi Mathieu,
This bug is now fixed in the SVN trunk.
Sorry for the delay it was a tricky one.
Thanks to have seen it.
Cheers,
Olivier

6

Thanks for spending your time investigating! :wink:
Cheers,
Z