Re: Extacting Likelihood for a fit to TH1

From: Rene Brun <brun_at_pcroot.cern.ch>
Date: Tue, 5 Jul 2005 16:38:46 +0200 (MEST)


Hi Jeanne,

When using Minuit, you can use gMinuit->fAmin This TMinuit member contains the value of the minimum of the Likelihood function.
Note that in the pro version the value printed by Minuit FCN is the equivalent chisquare and not the true minimum as available in gMinuit->fAmin.
In the CVS version, I have modified the print routine from Minuit to print the right value.

Rene Brun

On Fri, 1 Jul 2005, Jeanne
Wilson wrote:

> Hello,
> I am running root Version 4.01/03 on Fedora Core 2 and am
> performing a likelihood fit on a histogram. Since chisquared breaks down
> in the low statistics limit, I want to extract the maximum likelihood as
> a figure of merit for the fit. MINUIT returns the value I want to screen
> "FCN=..." but how do I access this value in a macro?
>
> Here is a simplified example:
>
> TF1 *func = new TF1("func", "[0]",0,100);
> TH1F* htot = new TH1F("htot "," ",100,0,100);
> for(Int_t j=0;j<200;j++){
> htot->Fill(100*gRandom->Uniform(0.0,1.0));
> }
> htot->Fit("func","L");
>
> which outputs to screen:
>
> FCN=340.813 FROM MIGRAD STATUS=CONVERGED 56 CALLS 57
> TOTAL
> EDM=7.22708e-12 STRATEGY= 1 ERROR MATRIX
> ACCURATE
> EXT PARAMETER STEP FIRST
> NO. NAME VALUE ERROR SIZE DERIVATIVE
> 1 p0 2.00000e+00 1.41421e-01 1.27663e-03 -2.68832e-05
>
> I would like to access FCN=340.813.
>
> Cheers,
> Jeanne Wilson
>
Received on Tue Jul 05 2005 - 16:39:03 MEST

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