mrhistmatch: Use normal equation
mrhistmatch: Use normal equation

The previous code was observed to return a unity scaling factor for some data despite the clear presence of variability in image intensity between the input and target images. Utilising the normal equation resulted in sensible scaling factors for these data.

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