Multithreading in ROOT::Fit::Fitter::FitFCN?

ROOT
1

Hi,

I found somewhere in another forum topic the recommendation to use

fitter.Fit(data, ROOT::EExecutionPolicy::kMultiThread );

for enabeling multithreading in ROOT::Fit::Fitter::Fit. I’m currently using in my fitting class TSimuFit the functor approach for a user defined fit function:

  fFit = new Fitter();
  fFit->SetFCN(npar, *this, &vinit[0], 0, fFitType);
  ...
  fFit->FitFCN();

where the class implements double TSimuFit::operator()(const double* par). The (binned or unbinned) data is a class member variable.

Is there a possibility to use the ROOT::EExecutionPolicy::kMultiThread also in this case? To be honest, I’m a little overwhelmed by the many Fitter::Fit and Fitter::FitFCN variants in the interface, but I don’t see any FitFCN that allows to set a ROOT::EExecutionPolicy.

Best and thanks,
Klaus

ROOT Version: 6.36.04
Platform: Linux Mint 21
Compiler: Not Provided

2

Hi @canigia ,

Adding @Danilo and @jonas in the loop who can help answer your question.

Cheers,
Aaron

3

Thanks for you quick reply!

I think I meanwhile found my own error in reasoning. Since my user function loops the data and evaluates the fit model with given parameters itself, there is no simple opportunity for multithreading (by splitting the data into chunks) anymore. So I would like to rephrase my question:

  • I’d like to implement a simultaneous fit class, that evaluates a set of fit functions sharing several parameters on a set of individual data sets, either binned (histogram bin contents with errors) or unbinned (vector of double). The obvious opportunity for multithreading is splitting the data and evaluating the fit functions in parallel.

Is there a elegant way to do so using Fitter::Fit(..) with ROOT::EExecutionPolicy::kMultiThread enabled?