mrmath: rewrote variance to avoid catastrophic cancellation. \n\ndouble checked with numpy.var with 64bit precision data for small and large numbers
mrmath: rewrote variance to avoid catastrophic cancellation. \n\ndouble checked with numpy.var with 64bit precision data for small and large numbers

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3