def bend_cos(rs, deriv=<NUM_LIT:0>):
return _bend_transform(rs, _bend_cos_low, deriv)<EOL>
Compute the cosine of the angle between the vectors rs[0]-rs[1] and rs[2]-rs[1]

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

       When derivatives are computed a tuple with a single result is returned