docs: def surf_vol(length, girth):
      '''Calculate the surface volume of an animal from its length and girth
  
      Args
      ----
      length: float or ndarray
          Length of animal (m)
      girth: float or ndarray
          Girth of animal (m)
  
      Returns
      -------
      surf:
          Surface area of animal (m^2)
      vol: float or ndarray
          Volume of animal (m^3)
      '''
      import numpy
  
      a_r   = 0.01 * girth / (2 * numpy.pi)
      stl_l = 0.01 * length
      c_r   = stl_l / 2
      e    = numpy.sqrt(1-(a_r**2/c_r**2))
  
      surf = ((2*numpy.pi * a_r**2) + \
             (2*numpy.pi * ((a_r * c_r)/e)) * 1/(numpy.sin(e)))
  
      vol  = (((4/3) * numpy.pi)*(a_r**2) * c_r)
  
      return surf, vol