RF: _directional_kurtosis to directional_kurtosis gtol=1e-5 -> gtol=1e-2 to speed performance
RF: _directional_kurtosis to directional_kurtosis
gtol=1e-5 -> gtol=1e-2 to speed performance

FrancoisRheaultUS/dipy,nilgoyyou/dipy,FrancoisRheaultUS/dipy,nilgoyyou/dipy