[ROOT] Double-GAUS fit

From: Alberto Pulvirenti (alberto.pulvirenti@ct.infn.it)
Date: Wed Jul 28 2004 - 10:20:04 MEST

Dear all,

I have made a study where I needed to manage a histogram which should 
have a shape which is the result of the superimposition of two distinct 
gaussians, with similar mean (around 0) and very different constant & 
sigma values.

I managed to realize a macro which performs the fit of two gaussians, 
which is initialized first excluding the 'signal' events (the higher and 
narrower one), and fitting the background. Then, I excluded such 
background and fitted the signal.
Finally, using the values obtained from these partial fits, I generated 
a function which i just the sum of two gaussians, and I refitted it.

Of course, the result can be approximative (sometimes I get large chi 
square). A colleague of mine told me that in PAW there was an automatic 
procedure to perform a double-gaussian fit. I was wondering if such a 
procedure is present also in ROOT or not.

Another question about fit is the following. We know that in a 
normalized gaussian there is a precise relationship between the constant 
and sigma, and then such a function has only two (not three) free 
parameters. Is there any "automatic" function which performs this?


Alberto Pulvirenti, Ph. D.
University of Catania / INFN Catania
Address: Via S. Sofia, 64 I-95123 Catania
   Phone: +39-095-378-5286

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