====================================================
              Test of fastmath
====================================================
sub_v_vT_m: the slow and fast way
[[-41 -52 -63]
 [-59 -76 -93]
 [-14 -19 -24]]
[[-41 -52 -63]
 [-59 -76 -93]
 [-14 -19 -24]]

sub_m_v_vT: the slow and fast way
[[-21 -31 -8]
 [-54 -82 -23]
 [-87 -133 -38]]
[[-21 -31 -8]
 [-54 -82 -23]
 [-87 -133 -38]]