CONAN.utils.cosine_atm_variation
================================

.. py:function:: CONAN.utils.cosine_atm_variation(phi, Fd=0, Fn=0, delta_deg=0, cosine_order=1)

   Calculate the phase curve of a planet approximated by a cosine function from Fmin to Fmax
   The equation is given as F = Fmin + (Fmax-Fmin)/2*(1-cos(phi + delta)). The semi-amplitude of the atmospheric phase variation  is (Fmax-Fmin)/2,
   phi is the phase angle of the planet (true anomaly+omega-pi/2) in radians, and delta is the hotspot offset (in radians).
   Fday and Fnight are obtained as the value of F at phi=pi and 0 respectively.


   :param phi: phase angle (2*pi*phase for circular orbit) or true anomaly+omega-pi/2 in radians.
   :type phi: array-like
   :param Fd: Dayside flux/occultation depth
   :type Fd: float
   :param Fn: night side flux
   :type Fn: float
   :param delta_deg: hotspot offset in degrees. Positive values indicate eastward offset (peak before secondary eclipse).
   :type delta_deg: float
   :param cosine_order: order of the cosine function. Default is 1
   :type cosine_order: float/int;

   :returns: **F** -- planetary flux as a function of phase
   :rtype: array-like