[ROOT] Problem with errors in TMinuit

From: catutza@mps.ohio-state.edu
Date: Wed Jul 12 2000 - 00:06:14 MEST


Hi Rooters,

I have a question regarding TMinuit.

I have two Monte Carlo histograms (signal and background), and I am
generating a fake data histogram by drawing N1 'events' out of the signal
histogram, and N2 from the background histogram.  
I use then TMinuit to fit the fake data as the sum of the two MC histos -
to see if I get numbers close to N1 and N2.

I do this many times; the fit always returns about the right value for N1
and N2. However, the error returned by the fit appears to be the same 
every time (it slightly varies within a very small range).

Has anybody seen this (or something similar) before? Is there a bug in the
way the errors on the parameters are computed?
I am using ROOT Version 2.22/06.

Thanks for the help,

Catalin Ciobanu, CDF
e-mail: catutza@mps.ohio-state.edu



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