Use gPad->GetUymax in this case. Make sure that gPad
points to the pad.
Remember that in a macro, the following logic is not sufficient:
{
TCanvas *c = new TCanvas();
h->Draw();
gPad->GetUymax();
}
At the time you call gPad->GetUymax, the histogram has not yet been paint.
The Draw function simply adds a reference to the histogram in the list of
primitives. You must force the histogram to be paint with:
{
TCanvas *c = new TCanvas();
h->Draw();
c->Update();
gPad->GetUymax();
}
see: http://root.cern.ch/root/HowtoDraw.html
Rene Brun
On Thu, 3 Oct 2002, Guillaume Blanc wrote:
> Hi,
>
> Actually this is not the maximum value of the histogram I want, but the
> maximum value of the Y axis on the pad, which is about h->GetMaximum() + 10%.
> Is there something to get this value precisely?
>
> Or: how to put an second X axis exactly on top on the plot?
> TGaxis constructor asks for xmin, ymin, xmax, ymax values... I can get the
> xmin, xmax values from h->GetXaxis()->GetXmin() and GetXmax(), but I can't
> for the ymin,ymax values...
>
> Guillaume Blanc
>
>
> On Wed, 2 Oct 2002, Rene Brun wrote:
>
> > Hi,
> >
> > I assume that you want to access the maximum value of a histogram and
> > not the maximum value in Y of the pad. If yes, use
> > h->GetMaximum();
> >
> > Rene Brun
> >
> > On Thu, 3 Oct 2002, Guillaume Blanc wrote:
> >
> > > Hello,
> > >
> > > Perhaps this question is obvious, but I would like to get the max value on
> > > the Y axis of a TH1F histo. I tried : h->GetYaxis()->GetXmax() but it
> > > doesn't work (return a wrong value); note that the equivalent command
> > > works for the X axis. And gPad->GetUymax() returns also a
> > > wrong value (closer to the one expected, but still wrong)...
> > > I just would to add another X axis on top of my plot with a different
> > > scale: I need the Y axis max value in order to position it accurately...
> > >
> > > Well, if anybody has a idea!
> > >
> > > Thanks for your help,
> > >
> > > Guillaume Blanc
> > >
> >
> >
>
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