RE: Map the chi2

From: Manuel Mussini <Manuel.Mussini_at_bo.infn.it>
Date: Tue, 11 Mar 2008 08:00:51 +0100

Hi Lorenzo,
contours scans only "near" the found minimum so I think it isn't the right choice for searching for another eventual "far" minimum! I've never tried SCAN! I'll do it as my next step! Is it possible to scan "by hand"? I mean ... can I fix all my 3 parameters and evaluate the chi2? With TMinuit::FixParameter(Int_t) I think I can get the first part but ... how to update the chi2?
The best result would be to obtain a 3D histo showing the chi2 surface (for each parameters couple)!

Bye…

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From: Lorenzo Moneta [mailto:Lorenzo.Moneta_at_cern.ch] Sent: Monday, March 10, 2008 23:14
To: Manuel Mussini
Cc: roottalk_at_lxbuild091.cern.ch
Subject: Re: [ROOT] Map the chi2

Hi Manuel,

 you can either scan a single parameter around the minimum, (command SCAN in
Minuit) or build contours for two parameters, like in fitcont.C.  I think contours will give you the best way for maping the  chi2 around the minimum. 

 Cheers

 Lorenzo 

On Mar 10, 2008, at 7:20 PM, Manuel Mussini wrote:

Hi,
I have a TH1D and a 3 parameters user defined TF1 to fit it. Which is the best way to map the chi2 around the convergence point? I thoughed to map the 3 parameters in pairs (fix one of them and scan the other two) but it not so clear (to me!) how to implement the mapping! I’ve tried the fitcont.C tutorial but this is not what I want!
 

Thanks!!!
 

Bye… Received on Tue Mar 11 2008 - 08:01:14 CET