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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