Re: [ROOT] Fitting Option and Errors.

From: Arthur E. Snyder (
Date: Fri Oct 08 2004 - 05:44:05 MEST

My understandin is that the "I" option perdicts the number of events in a
bin by doing the proper integration over the bin whereas the normal method
(like paw) just uses the  value at the center of the bin times the bin
width. If the function does not vary much over the size of the bin these
method will be nearly equivalent; if the function varies a lot within the
bin, the center-of-bin method is suspect and one would expect a larger
difference ..


----- Original Message ----- 
From: "zaldy" <>
To: <>
Sent: Wednesday, October 06, 2004 11:41 PM
Subject: [ROOT] Fitting Option and Errors.

> Dear folks,
> I am just wondering why the result (particularly the fitted
> parameter errors) of
> (a) TH1::Fit("myFunc") and
> (b) H1::Fit("myFunc","I")
> seems to have little difference (~1% or less).
> I expect a larger difference (not at this 1% level) since (b) accounts the
> bin errors (???)
> My questions:
> 1. In (a), what or how is the bin errors used in the fitting?
>    Is this the default (sqrt of bin content?)
> 2. In (b), how do we qoute the fitted parameters if we change the option
> to "E"? I noticed that the MINOS errors(NEGATIVE/POSITIVE) are not exactly
> same (at least slightly differ).
> Like to understand these points. Any Hints?
> Thanks in Advance...
> -- 
> Zaldy A. Nawang

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