Hi,Rene,
You know ,I fill the histogram from the root file which does not store
error infomation.
kskp->Draw("Mass>>etac","Ccen<0.6&&Pt<0.6&&abs(Ksmass-0.497672)<0.010");
If this means i should check the error of the histogram
bins (I suppose it should be caculated automatically) when i fill a
histogram from root(ntuple) file? It confused me.
I also noticed if i more tighter cut, the fit quality worse. You know
different cut means got differnet histogram. But if i loose cut and no
no empty bins inhistogram,root got same result with mn_fit.
A senior professor said that mn_fit had same problem before.
Gong Datao
On Wed, 26 Feb 2003, Rene Brun wrote:
> Hi Gong,
>
> I looked at your histogram. You have a few points for which the errors
> do not seem correct. I do not know how you filled your histogram.
> If you add the 3 following lines
> etac->SetBinError(18,20);
> etac->SetBinError(23,20);
> etac->SetBinError(43,20);
>
> to set bigger error bars for these 3 bins and fit with the simple
> loglikelihood method
> his->Fit(FunName,"L0");
>
> then you will get a chi2/ndf = 190/189
>
> Rene Brun
>
> On
> Wed, 26 Feb 2003, Datao Gong wrote:
>
> > Hi,Rooters,
> > I fit my ntuple with likelihood method. I found if i tightly cut,
> > the fit result is much different and fit quality worse (ch2/ndf far
> > away from 1). Compare to min_fit, i found it is from the empty bins
> > in histogram. Likelihood method seems do not take into account
> > empty bin default. (I read Burn's email in roottalk02). In my case,
> > I fit my histogram with option "EMVL0", the ch2/ndf is 237/189, meanwhile,
> > mn_fit give me 190/191. I know there are two empty bins in my histogram.
> > If i set "W" option, the chi2/ndf is up to 3067/191. Is there something
> > wrong?
> >
> > Gong Datao
> >
> >
>
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