If determ, trace or first is given
M is scaled such that its determinant, trace or first diagonal
element, respectively, equals that value. If none of the three is
given M is scaled such that its determinant equals one. If more
than one criteria is given the first of them is used and the others
silently ignored.
References
Paindaveine D. (2008) A Canonical Definition of Shape. Statistics and Probability Letters 78, 2240-2247