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Description
When fitting a TGraphErrors, with errors in the x coordinate, there is currently no support to perform the operation using milt-threads as it is currently done for TH1::Fit or TGraph::Fit.
One needs to use the TThreadExecutor in the `FitUtil::EvsluateEffectiveChi2 function.
This has been requested in https://root-forum.cern.ch/t/multithreading-on-minuit/46225/13