Hi,
Thanks for reporting this interesting problem with fitting.
The problem appears only with the Log likelihood method.
I have fixed the problem in TFitter::GetSumLog in the development version
in CVS. The fix will be part of 3.00/05.
Rene Brun
Altenburg wrote:
>
> // Hi all,
>
> // i think i've got a problem in fitting histograms.
> // I 've fitted a histogram interactively using a third order polynom.
>
> root [0] TFile *hist = new TFile("histos.root")
> root [1] TF1 *Back2 = new
> TF1("Back2","[0]+[1]*x+[2]*x*x+[3]*x*x*x",0.4,0.7)
> root [2] Back2->SetParameters(300.,-100.,150.,10.)
> root [3] ContEta2->Fit("Back2","RL")
>
> FCN=-32092.9 FROM MIGRAD STATUS=CONVERGED 272 CALLS 273
> TOTAL
> EDM=4.73204e-08 STRATEGY= 1 ERROR MATRIX
> ACCURATE
> EXT PARAMETER STEP FIRST
> NO. NAME VALUE ERROR SIZE DERIVATIVE
> 1 p0 -1.46319e+04 6.90699e+01 3.44556e-01 -7.34782e-05
>
> 2 p1 9.80068e+04 2.12779e+02 5.88180e-01 -4.20585e-05
>
> 3 p2 -1.80068e+05 3.29361e+02 9.65728e-01 -2.48735e-05
>
> 4 p3 1.02277e+05 3.37668e+02 1.54092e+00 -1.52108e-05
>
> root [4] .q
>
> // Then i've started a new session and fitted another histo.
>
> root [0] TFile *hist = new TFile("histos.root")
> root [1] TF1 *Back1 = new
> TF1("Back1","[0]+[1]*x+[2]*x*x+[3]*x*x*x",0.4,0.7)
> root [2] Back1->SetParameters(300.,-100.,150.,10.)
> root [3] ContEta1->Fit("Back1","RL")
>
> FCN=-22590.4 FROM MIGRAD STATUS=CONVERGED 265 CALLS 266
> TOTAL
> EDM=7.3406e-09 STRATEGY= 1 ERROR MATRIX
> ACCURATE
> EXT PARAMETER STEP FIRST
> NO. NAME VALUE ERROR SIZE DERIVATIVE
> 1 p0 -5.82500e+03 5.45431e+01 2.32862e-01 -3.24646e-05
>
> 2 p1 4.76081e+04 1.65389e+02 3.94822e-01 -1.73923e-05
>
> 3 p2 -9.38529e+04 2.53567e+02 6.45203e-01 -9.44618e-06
>
> 4 p3 5.53770e+04 2.62867e+02 1.02632e+00 -5.23026e-06
>
> root [4] TF1 *Back2 = new
> TF1("Back2","[0]+[1]*x+[2]*x*x+[3]*x*x*x",0.4,0.7)
> root [5] Back2->SetParameters(300.,-100.,150.,10.)
> root [6] ContEta2->Fit("Back2","RL")
>
> FCN=-1.60236e+06 FROM MIGRAD STATUS=CONVERGED 301 CALLS
> 302
> TOTAL
> EDM=2.28043e-06 STRATEGY= 1 ERROR MATRIX
> ACCURATE
> EXT PARAMETER STEP FIRST
> NO. NAME VALUE ERROR SIZE DERIVATIVE
> 1 p0 -1.46317e+04 3.17154e+01 2.43464e+00 5.26951e-04
>
> 2 p1 9.80057e+04 8.68069e+01 4.15614e+00 3.15050e-04
>
> 3 p2 -1.80066e+05 1.28650e+02 6.82403e+00 1.92549e-04
>
> 4 p3 1.02276e+05 1.49180e+02 1.08886e+01 1.19699e-04
>
> // As you can see the parameters for ContEta2 are not equal. Note , i've
> used
> // the same histogram, fit-function, start parameters and range.
> // I've also tried to set the errors via "SetParError", but it didn't
> solve the
> // problem.
>
> // I'm waiting for reply.
> // Thanks.
>
> --------------------------------------------------------------------------------
>
> Name: histos.root
> histos.root Type: unspecified type (application/octet-stream)
> Encoding: base64
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