docs: def square(m, eff_max,c,m0,sigma,m1=21):
      """
      eff_max:  Maximum of the efficiency function (peak efficiency)
      c: shape of the drop-off in the efficiency at bright end
      m0: transition to tappering at faint magnitudes
      sigma: width of the transition in efficeincy
      m1: magnitude at which peak efficeincy occurs
  
      square(m) = (eff_max-c*(m-21)**2)/(1+exp((m-M_0)/sig))
      """
  
      return (eff_max-c*(m-21)**2)/(1+numpy.exp((m-m0)/sigma))