Re: gMinuit problem ..

From: Rene Brun <Rene.Brun_at_cern.ch>
Date: Sat, 28 Feb 2009 09:37:51 +0100


Art,

When fitting with simple functions like polynomials, TMinuit is not used, only the linear fitter (TLinearFitter). The linear fitter is much faster than Minuit. You can force fitting of a polynomial with Minuit by specifying the fit option "L", see documentation of TH1::Fit

Rene Brun

Arthur E. Snyder wrote:
>
> Rene et al.,
>
> We are seeing strange behavior with gMinuit. It seems to come and go.
> I expect it to be there after I do it fit.
>
> An example:
>
> I have a histogram (it doesn't matter what it is).
>
> root [26] h->Fit("pol4")
> Fitting results:
> Parameters:
> NO. VALUE ERROR
> 0 2.625170e+03 1.191186e+02
> 1 -1.565262e+04 1.055977e+03
> 2 3.861477e+04 3.327115e+03
> 3 -4.315887e+04 4.446220e+03
> 4 1.804345e+04 2.140152e+03
> (Int_t)0
> root [27] gMinuit
> (class TMinuit*)0x0
> root [28]
>
> -->gMinuit is MIA
>
> root [28] h->Fit("gaus")
> FCN=687.968 FROM MIGRAD STATUS=CONVERGED 3927 CALLS 3928
> TOTAL
> EDM=5.19353e-06 STRATEGY= 1 ERR MATRIX
> NOT POS-DEF
> EXT PARAMETER APPROXIMATE STEP FIRST
> NO. NAME VALUE ERROR SIZE DERIVATIVE
> 1 Constant 1.93812e+09 1.54608e+08 9.24169e+02 2.24749e-10
> 2 Mean -8.98813e+00 2.37909e-02 2.18708e-05 1.46725e+00
> 3 Sigma 1.67356e+00 3.02321e-02 2.53915e-03** at limit **
> (Int_t)0
> root [29] gMinuit
> (class TMinuit*)0x9486650
>
> -->gMinuit is there!
>
> In a more complex sitution where we construct a simple TF1 in a macro,
> gMinuit is sometimes there and sometimes not -- seemingly w/o reason --
>
> -Art S.
>
>
>
> A.E. Snyder, Group EC \!c*p?/
> SLAC Mail Stop #95 ((. .))
> Box 4349 |
> Stanford, Ca, USA, 94309 '\|/`
> e-mail:snyder_at_slac.stanford.edu o
> phone:650-926-2701 _
> http://www.slac.stanford.edu/~snyder BaBar
> FAX:650-926-2657 Collaboration
>
>
>
Received on Sat Feb 28 2009 - 09:38:00 CET

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