def dihed_cos(rs, deriv=<NUM_LIT:0>):
return _dihed_transform(rs, _dihed_cos_low, deriv)<EOL>
Compute the cosine of the angle between the planes rs[0], rs[1], rs[2] and rs[1], rs[2], rs[3]

       Arguments:
        | ``rs``  --  four numpy array with three elements
        | ``deriv``  --  the derivatives to be computed: 0, 1 or 2 [default=0]