text: from __future__ import division
  import numpy as np
  __all__ = ["q2InclinationAngle"]
  
  def q2InclinationAngle(q, q0=0.2):
      """
      Calculate the inclination angle from the axis ratio.
  
      Parameters
      ----------
      q : array like
          The axis ratio, b/a.
      q0 : float
          The intrinsic axis ratio when the galaxy is edge-on.
  
      Returns
      -------
      i : array like
          The inclination angle, units: radian.
  
      Notes
      -----
      The equation is from Topal et al. (2018MNRAS.479.3319T), equation (1).
      """
      i = np.arccos(np.sqrt( (q**2 - q0**2) / (1.0 - q0**2) ))
      return i
  