Dear Rene, Rooters, I put in attachment two files, the first one is histo.root which contain the histogramm (named "h37") I try to fit and the second is testfit.C which is a reduced version of the macro I use. This macro do two differents fits on the same plot (which is duplicated using the clone method of TH1F). I put hardwarely the fit parameters which made the matrix to not be defined positively but in the initial macro these are calculated from the parameters returned by the first fit. I made this test macro quickly so just tell me whether I have to put the calculation of the new parameters step in this step macro. Thank you for your help, Best regards, Sebastien Rene Brun a écrit : >Hi Sebastien, > >As explained by Eddy, it looks like your parameters are correlated. >Could you send a small file containing your histogram, plus >a short test macro? > >Rene Brun > >On Thu, >13 May 2004, Sébastien Gadrat wrote: > > > >>Hi Rooters, >> >>I get a strange error message when fitting some mass plots. Among >>information returned by Minuit after the completion of the fit, I get >>"ERR MATRIX NOT POS-DEF" ! I have read in Minuit documentation the need >>for a positive defined matrix around the minimum for a "physical" >>function. I use the same method to fit five different mass spectra >>(differents cuts are used to generate each of these mass spectra) and >>only one fit returned this error message. So I think the parametrization >>is good. According to Minuit documentation, it could also be due to a >>numerical inaccuracies or a non-physical region. What can I do to >>distinguish between these two possibilities and to get a positived >>defined matrix ? >> >>Here is the output I get for this fit (the fit function is made of three >>exponentials): >> >>FCN=153.796 FROM MIGRAD STATUS=CONVERGED 91 CALLS 92 TOTAL >> EDM=2.47125e-08 STRATEGY= 1 ERR MATRIX NOT >>POS-DEF >> EXT PARAMETER APPROXIMATE STEP FIRST >> NO. NAME VALUE ERROR SIZE DERIVATIVE >> 1 const0 5.72969e+03 7.36832e+01 4.07529e-01 -1.22906e-06 >> 2 const1 -8.46984e-01 7.65250e-03 3.44875e-06 7.87522e-02 >> 3 const3 9.15351e-02 7.21665e-03 1.82483e-05 -4.06709e-02 >> 4 slope1 2.19718e+00 6.64370e-03 2.93137e-06 -4.12211e-02 >> 5 slope2 2.08281e+00 6.22503e-03 2.84950e-06 4.62693e-02 >> 6 slope3 5.18135e-01 1.17508e-02 3.77755e-05 7.06570e-03 >> >>Thanks in advance, >>Regards, >> >>Sebastien >> >> >> > > >
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