y=lab.cross(a,b)
returns the cross product of the tensors a and b.
a and b must be 3 element vectors.
y=cross(a,b)
returns the cross product of a and b along the first dimension of length 3.
y=cross(a,b,n)
, where a and b returns the cross
product of vectors in dimension n of a and b.
a and b must have the same size,
and both a:size(n) and b:size(n) must be 3.