// 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.
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