I can now access the error matrix through pyROOT, thanks to the efforts of Rene and Wim. The following works, having built root from CVS: import ROOT h = ROOT.TH1F("h","test",100,-2,2) h.FillRandom("gaus",1000) h.Fit("gaus") fitter = ROOT.TVirtualFitter.GetFitter( ROOT.TVirtualFitter() ) fitter.GetCovarianceMatrixElement(0,1) Yea! Many thanks to you for getting this to work! I can also access gMinuit via: gMinuit = ROOT.gROOT.GetGlobal( "gMinuit", 1 ) Current problems: (These don't bother me so much now that I have a way into the covariance matrix) I can't do anything much with gMinuit though. I'd have expected the following to print out the covariance matrix, for example: >>> gMinuit.mnexcm("SHO COV") Traceback (most recent call last): File "<stdin>", line 1, in ? SystemError: NULL result without error in PyObject_Call Seems like all other (useful) methods of gMinuit have similar problems. GetName() works. So I haven't been able to populate a TMatrixD yet, and if I did I'm not sure I could access the elements of it. But here I'm just playing around. Another thing that doesn't work but should: >>> covm = ROOT.TMatrixD(3, 3, fitter.GetCovarianceMatrix()) Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: None of the 15 overloaded methods succeeded That's all for now. Topher Cawlfield
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