Re: [ROOT] TMultiGraph fit gives me a bad chi square.

From: Rene Brun (Rene.Brun@cern.ch)
Date: Mon Nov 17 2003 - 18:11:35 MET


Venkatesh Kaushik wrote:
> 
> Hi,
> 
> The values on the X- axis are in GeV, whereas the ones on the
> Y-axis are in MeV, so i multiplied the errors and mean-values
> on Y-axis by 0.001. to make both the axes be in same units. 

>Is that a mistake?

Yes. You are likely missing a sqrt somewhere

Rene Brun


> Venkat
> 
> On Mon, 17 Nov 2003, Rene Brun wrote:
> 
> > Hi,
> >
> > Your errors cannot be right. They are far too small. This makes the chisquare
> > too big.
> > Why do you multiply the errors by 0.001 ?
> >
> > Rene Brun
> >
> > Venkatesh Kaushik wrote:
> > >
> > >  Hi ROOTers,
> > >  I have two sets of data points, which I am supposed to fit straights line
> > >  to. I try to fit both these with pol1, I observe two things
> > >  1) the chi square / dof value is horrible.
> > >  2) visually, i don't see the fit has done a good job.
> > >
> > >  i am not sure what's happening. are there any default fit
> > >  strategies/parameters that is messing up my fit?
> > >
> > > I have attached my code and the program output for your kind perusal.
> > > Thanks for the help.
> > > Venkat.
> > >
> > >   --------------------------------------------------------------------------------
> > >                          Name: Eliveonly_ecal.gif
> > >    Eliveonly_ecal.gif    Type: GIF Image (IMAGE/gif)
> > >                      Encoding: BASE64
> > >
> > >                   Name: Ecal_live.C
> > >    Ecal_live.C    Type: Plain Text (TEXT/PLAIN)
> > >               Encoding: BASE64
> >



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