Thanks Rene, I have been looking at http://root.cern.ch/root/html/TH1.htm and didn't see this very clear discussion. Sorry: I always feel silly when I miss a well-documented fact. I will try the full-blown TVirtualFitter method that I was hoping to avoid. (What should I have typed into the "search the root reference guide" window to find the TF1 doc you mentioned? Your excerpt is actually not in the TH1.htm page that I have been using as a reference, nor in the "fitting with a user-defined function" etc. pages in the ref guide. I also didn't see it in the User's Guide 3.02c. A new source of documentation is always welcome...what is the origin of that excerpt?) - John Rene Brun wrote: > Hi John, > > The TF1 doc has this remark: > > // > // WHY TF1 CANNOT ACCEPT A CLASS MEMBER FUNCTION ? > // =============================================== > // This is a frequently asked question. > // C++ is a strongly typed language. There is no way for TF1 (without > // recompiling this class) to know about all possible user defined data types. > // This also apply to the case of a static class function. > > > In the C-style function referenced by TF1 and called from TH1::Fit, > you can call your class member function. > You can either use a global to access an object of your class > or use TVirtualFitter::SetUserFunc to register the address of a TObject* > to the fitter. In the C-style function, you can retrieve this pointer > with something like: > TObject *myobject = TVirtualfitter::GetFitter()->GetUserFunc(); > > Rene Brun > > > "Dr. John Krane" wrote: > >>Hi, >> >>I'm trying to use weighted histograms to fit a distribution. Because I >>want to be able to change the histos that I'm using as components, I >>made a little class that holds an array of TH1F. A member function >>provides the weighted sum of these histograms, with the weights being >>the fit parameters and the interface being as required by TF1. So I >>tried to make a TF1 for use with the ->Fit method, like this: >> >> cerr<< "Assign the histos that contribute to fit"<<endl; >> func_fit fclass; >> fclass.add_param(d1or); //first histo >> fclass.add_param(d1crl); //second histo...etc. >> >> TF1 *fitFcn = new >> TF1("fitFcn",fclass.func_val,-600.,-1.,fclass.get_nparam()); >> >>Well the compiler within ROOT doesn't like that, so I tried making a >>pointer-to-member-function and giving that to root, but I didn't get >>anywhere. Does anybody know how to provide a member-function to TF1? I >>think my class solution is quite clean for what I'd like to do, but I >>need to get around this barrier... >> >> - John > > >
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