Hello, I have new problem with fitting unsorted data. I am trying to fit unsorted array X,Y to line. I use object TGraph. Parameters of line is well, but error is very strange. Test macro with only 5 data point. (In real life number of data point is larger, but problem still exist): { float Xarr[5]; float Yarr[5]; Xarr[0] = 0.062893; Yarr[0] = 0.584000; Xarr[1] = 0.000000; Yarr[1] = 0.646000; Xarr[2] = 0.062893; Yarr[2] = 0.572000; Xarr[3] = 0.125786; Yarr[3] = 0.497000; Xarr[4] = 0.125786; Yarr[4] = 0.533000; // Xarr[5] = 0.000000; Yarr[5] = 0.626000; // Xarr[6] = 0.125786; Yarr[6] = 0.529000; // Xarr[7] = 0.251572; Yarr[7] = 0.432000; // Xarr[8] = 0.125786; Yarr[8] = 0.534000; // Xarr[9] = 0.251572; Yarr[9] = 0.441000; // Xarr[10] = 0.188679; Yarr[10] = 0.480000; // Xarr[11] = 0.000000; Yarr[11] = 0.627000; // Xarr[12] = 0.377358; Yarr[12] = 0.338000; // Xarr[13] = 0.188679; Yarr[13] = 0.467000; // Xarr[14] = 0.251572; Yarr[14] = 0.405000; // Xarr[15] = 0.000000; Yarr[15] = 0.646000; // Xarr[16] = 0.503145; Yarr[16] = 0.252000; // Xarr[17] = 0.251572; Yarr[17] = 0.366000; c1 = new TCanvas("c1","proba"); TF1 *f1 = new TF1("f1","pol1"); f1->SetRange(0,0.15); TGraph *tg = new TGraph(5, Xarr, Yarr); tg->Fit("f1","R","AP"); tg->Draw("A*"); } Result of fitting: p0 = 0.64 +- 0.85 !, p1 = -1.04 +- 9.5 !!! Where is error? It is my error or not? I use ROOT 1.02/00 1 august 1997 ( Valery Fine version) on Windows NT With best regards Voropaev S.G.
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