Re: [ROOT] log-scale and TH1::Fit

From: Rene Brun (Rene.Brun@cern.ch)
Date: Mon Oct 29 2001 - 16:28:39 MET


Hi Thomas,

Well, obviously, you should not fit with a "gaussian" what is not a gaussian.
You should define a function with the right variable.

What I could do automatically is the creation of the histogram with
the variable size bins computed with the logarithm.

Rene Brun

Thomas Bretz wrote:
> 
> Hi Rene,
> 
> I'm using a variable bin size histogram like you showed in your example.
> So I get the graphical output, as I like it. But if I try to fit this
> histogram with a gaussian the 'raw' data is fitted. But I want to fit
> the logarithmic data (3, 4, 5 not 1e3, 1e4, 1e5) The gaussian I get
> after calling TH1::Fit doesn't even look like a gaussian (for sure) when
> log scale is enabled.
> 
> I would like to have both advantages. The advatage of a nice display of
> the x-axis and the advantage, that I can fit the logarithmic data
> instead of the raw data.
> 
> Regards,
> Thomas.
> 
> Rene Brun wrote:
> > > I have a histogram which is filled with some data. The get a more
> > > conviniet view of the x-axis I set the bins of the histogram so, that if
> > > I call gPad->SetLogx() I get equidistant bins. Now I want to fit this
> > > view with a gaussian, but TH1::Fit fits the original data instead of the
> > > logarithmic data.
> > >
> > > Is it possible to get either the nice view of a log-scaled X-Axis if i
> > > would use equidistant bins and fill the histogram with log(data) or is
> > > it possible to tell the fitter, that it should fit the logarithmic data
> > > instead of the 'real' data in the histogram?



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