np.einsum('...j,...j->...', vf, vf).dtype
np.einsum('...j,...j->...', vf, vf, dtype=np.int64)[-1, -1, -1]
np.einsum('...j,...j->...', vf, vf, dtype=np.double)[-1, -1, -1]
fastest way to find the magnitude (length) squared of a vector field