chi2asym_stat_func

gammapy.spectrum.chi2asym_stat_func(data, model, staterror=None, syserror=None, weight=None)

Define asymmetric chi-square errors.

TODO: reference ROOT TGraphAsymErrors and add test against ROOT result.

To make it fit into the Sherpa scheme we do this hack: * staterror = statistical down error * syserror = statistical up error