Hi, due to unitvec function there is no possibility to store 'list' vector - it has to be np.array /ndarray, otherwise None is returned.

Due to fact there is no imput check maybe it will be nice to edit unitvec function so it will change list object to np.array, e.g:

def unitvec(vec):
 """
 Scale a vector to unit length. The only exception is the zero vector, which
 is returned back unchanged.
 """
 if isinstance(vec, list):
 vec = numpy.array(vec)
 ....

BR, Marcin