[ROOT] Help on TGraphErrors

From: Mina Nozar (nozarm@jlab.org)
Date: Mon Apr 02 2001 - 22:52:31 MEST 

Hi.

I'm producing a postscript file containing many pages, each with nine
plots in it.  Each plot is the outcome of using TGraphErrors.  Now, for
each plot, I would like to draw a line at a fixed
x range (xmin and xmax are known constants), but at a different y range
(ymin and ymax change from plot to plot).  I've tried to use
ComputeRange method of TGraphErrors with no
success, see below please....   Am I doing something wrong?

//==========================================
float* afMoment = new float[nEntries];
 float* afErrMoment = new float[nEntries];
 float* afMass = new float[nEntries];
 float* afErrMass = new float[nEntries];
.....
....    // inside a loop
....
TGraphErrors *gr = new TGraphErrors(nEntries, afMass, afMoment,
afErrMass, afErrMoment);
gr->SetTitle(szMom);
gr->Draw("ap");
gr->GetXaxis()->SetTitle("m ( #omega #pi^{-} )  [MeV]");
gr->Draw("ap");

Double_t min_mass, min_h, max_mass, max_h;
gr->ComputeRange(min_mass, min_h, max_mass, max_h);
cout << "min_h:   " << min_h <<  "max_h: ' << max_h << endl;       ====>
this line prints zero for min_h and min_max ????  why?

TLine *line1= new TLine(1235,min_h,1235,max_h);
line1->Draw();

//=========================================

Thanks,

mina

--
Mina Nozar

nozarm@jlab.org ----- Phone:(757)269-6391 ----- FAX:(757)269-5800
Thomas Jefferson National Accelerator Facility
MS 12H, 12000 Jefferson Ave. Newport News, VA 23606

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