code: def pgpdf(omega, b, psi, trunc=200):
      
      ns = np.arange(trunc)
      psi_ns = np.array([_psi_n(omega, n, b) for n in ns])
      pdf = np.sum(psi_ns, axis=0)
  
      # Account for tilting
      pdf *= _tilt(omega, b, psi)
  
      return pdf
docs: Approximate the density log PG(omega | b, psi) using a
      truncation of the density written as an infinite sum.
  
      :param omega: point at which to evaluate density
      :param b:   first parameter of PG
      :param psi: tilting of PG
      :param trunc: number of terms in sum