Zaldy, I do not understand any of your 3 questions. It look like you are confusing the parameter p1 with what you call "P2" Please send a concrete running piece of code illustrating your points. Rene Brun zaldy wrote: > > Dear Folks, > > I have already posted this stuff a fews ago in ROOTTalk but I still need > to understand a few things. I also read the manual in TMinuit. > I am doing the fitting and access the fitted parameters and errors > using two fitting option: > > (a) TH1D::Fit("f_name"); (b) TH1D::Fit("f_name","E"); > > As a cross check I dumped a few parameter values and their errors. > > -----------a-a-a-a-a-a-a-a-a-a-a-a-a-a------------------------------------------ > This is the result for (a) TH1D::Fit("f_name"); > LINE FIT(Data) > Slope: 0.00162291 +/- 0.000605578 <====== P0 > Int. : 0.644645 +/- 0.440121 <====== P1 > > FCN=274.613 FROM MIGRAD STATUS=CONVERGED 1185 CALLS 1186 TOTAL > EDM=7.07449e-07 STRATEGY= 1 ERROR MATRIX UNCERTAINTY 3.1 per cent > EXT PARAMETER STEP FIRST > NO. NAME VALUE ERROR SIZE DERIVATIVE > 1 p0 6.44645e-01 4.40121e-01 -2.79232e-05 1.24430e-04 > 2 p1 1.62291e-03 6.05578e-04 -1.92359e-08 2.48881e-01 > ------------------------------------------------------------------------------- > > --------b-b-b-b-b-b-b-b-b-b-b-b-b-b------------------------------------------- > This is the result for (b) TH1D::Fit("f_name","E"); > LINE FIT(Data) > Slope: 0.00162291 +/- 0.000605869 <===== P0 > Int. : 0.644645 +/- 0.445796 <===== P2 > > FCN=274.613 FROM MINOS STATUS=SUCCESSFUL 6620 CALLS 8331 TOTAL > EDM=4.59478e-07 STRATEGY= 1 ERROR MATRIX ACCURATE > EXT PARAMETER PARABOLIC MINOS ERRORS > NO. NAME VALUE ERROR NEGATIVE POSITIVE > 1 p0 6.44645e-01 4.45830e-01 -4.46699e-01 4.44894e-01 > 2 p1 1.62291e-03 6.05907e-04 -6.05686e-04 6.06052e-04 > -------------------------------------------------------------------------------- > > In (a) the errors are reflected there in the summary. > > In (b) the errors do not exactly match. > I mean 0.000605869(for P1) is almost > the same with 4.45830e-01 (if qouting the PARABOLIC), but not equal. > As a cross check, it is good to know that the errors you dumped are near > to the MINOS algorithm, but this could be confusing. > > I have 3 questions: > > (1) Since the TMinuit members are public, then I expect to have same > values with the one printed in the summary below. Am I Correct? > > (2) Why is the dumped values not reflected in (b)? > Or Is the method: f->GetParError(nth_param) not enough? > In that case the user will still add few more lines(i.e., TMinuit * > minuit = new TMinuit ......; minuit->GetWhatIwant() ....)...I wanted to > Know. > > (3) How do we qoute the errors in (b) when the dumped values are not > reflected in the print out summary? > The reason I use option (b) is because this gives a more reliable result. > > Thank you very much. > > Zaldy A. Nawang
This archive was generated by hypermail 2b29 : Sun Jan 02 2005 - 05:50:09 MET