# Re: [ROOT] statistical error of Intergation

From: Arthur E. Snyder (snyder@slac.stanford.edu)
Date: Sat Feb 28 2004 - 08:28:03 MET

This not really a root problem ... just propagation of errors. The peak P
(par[0])) is related to area by A=P*sigma*sqrt(2pi) (no integral function
needed!), so given error matrix on P and sigma it easy to compute error on
A.

----- Original Message -----
To: <roottalk@pcroot.cern.ch>
Cc: <ahmed1@rcf.rhic.bnl.gov>
Sent: Friday, February 27, 2004 6:18 PM
Subject: [ROOT] statistical error of Intergation

> Dear Rooters,
>
>   I am new to the list, and I have the following which I coud not figure
out
> how to do it under root. I'm fitting my J/psi peaks by a Gaussian function
:
> f=N*Exp[-(x-\bar{x})^2/2 sigma^2]. Then I utilized the function
> Integral(min,max) to find the area or the number of counts under this fit.
> .
> .
> .
> n[j]->Fit("Gaus","R");
> G->SetParameters(par[0],par[1],par[2]);
> float mean = par[1];
> float sigma = par[2];
> float mlo = mean-3.0*sigma;
> float mhi = mean+3.0*sigma;
> cout <<mean<<" and "<<sigma<<" and " <<mlo<<"and "<<mhi<<endl;
> float binw = n[j]->GetBinWidth(1);
> double COUNTS = G->Integral(mlo,mhi)/binw;
> .
> .
> .
>
>
> I need to know how to find the statistical error of the integral, i.e.
"COUNTS"
> in root.
>
> Thank you very much
>
> Ahmed.
>
>
>
>
>
> =====
> "EAST OR WEST, HOME IS BEST".
>
>  Ahmed Al-Jamel
>  Physics Department(http://www.physics.nmsu.edu)
>  New Mexico State University
>  Box 30001, MSC 3D
>  Las Cruces, NM 88003-8001
>  Tel (off): (505)-646-7614.
>  http://www.feynman.nmsu.edu
>  http://www.phenix.bnl.gov/phenix/WWW/publish/ahmed1/
>
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