calc_cos_gamma
==============

.. py:function:: luminet.black_hole_math.calc_cos_gamma(alpha: float, incl: float) -> float

   Calculate :math:`\cos(\gamma)`

   This is used in the argument of the Jacobi elliptic integrals.

   .. math::

      \cos(\gamma) = \frac{\cos(\alpha)}{\sqrt{\cos(\alpha)^2 + \frac{1}{\tan(\theta_0)^2}}}

   :Parameters: * **alpha** (*float*) -- Angle in the black hole frame
                * **incl** (*float*) -- Inclination of the observer :math:`\theta_0`

   :returns: *float* -- :math:`\cos(\gamma)`