Re: [ROOT] log scale axis range problem

From: Kate Scholberg (schol@mit.edu)
Date: Mon Nov 04 2002 - 20:43:33 MET 

> >
> > I suspect this is a simple problem.  I'm just trying to Draw a simple
> > 1D histogram with a log scale, and I'm having trouble getting a
> > sensible default range of values on the y-axis from the Draw method.  I
> > also don't seem to able to set the axis range by hand with e.g.
> >
> > hist->GetYaxis()->SetRange(min,max);


> //adchithist2->GetYaxis()->SetRange(0.01,10.);
> adchithist2->SetMinimum(0.01);
> adchithist2->SetMaximum(10);
> adchithist2->Draw();
> adchithist2->Print("all");


OK, this works.  But wouldn't it be a more sensible default behavior
to have the axis range automatically set correctly for a log plot?
Shouldn't the histograms know what their minimum and maximum (nonzero) values
are?  Is there a good reason why this doesn't work automatically?

But leaving that aside for the moment, I have another log scale plot
with a scaled histogram that isn't plotting correctly.  The simple
macro example is attached. Root 3.03/06 works but Root 3.03/08 and
beyond (including the latest version from the cvs repository) just
plot nothing at all, although it seems to choose a reasonable y-axis
(in all cases RH Linux 7.3).  It seems to matter what the value used
for scaling actually is. A bug?

Kate Scholberg
schol@mit.edu


------------------------------------------------------------

void Scaled_hist()
{

  TCanvas *c2 = new TCanvas("c2","TRD hit dE");
  c2->SetLogy(1);
  c2->SetFillColor(10);

  gStyle->SetOptStat(0);

  Int_t nbin = 200;
  Float_t firstbin = 0.;
  Float_t lastbin = 200.;

  TH1F *detrd = new TH1F("detrd","dE from TRD",nbin,firstbin,lastbin);

  Float_t sum=0.;

  for(int i=0;i<1000;i++){
   sum = Float_t(gRandom->Gaus(0,20));
   detrd->Fill(sum);
  }

  detrd->Scale(1./50.);

 detrd->SetMarkerColor(2);
 detrd->SetMarkerStyle(22);

 detrd->Draw("p");
}

This archive was generated by hypermail 2b29 : Sat Jan 04 2003 - 23:51:16 MET