code: def PorodGuinierPorod(q, a, alpha, Rg, beta):
      
      return PorodGuinierMulti(q, a, alpha, Rg, beta)
docs: Empirical Porod-Guinier-Porod scattering
  
      Inputs:
      -------
          ``q``: independent variable
          ``a``: factor of the first power-law branch
          ``alpha``: exponent of the first power-law branch
          ``Rg``: radius of gyration
          ``beta``: exponent of the second power-law branch
  
      Formula:
      --------
          ``a*q^alpha`` if ``q<q_sep1``. ``G * exp(-q^2*Rg^2/3)`` if
          ``q_sep1<q<q_sep2`` and ``b*q^beta`` if ``q_sep2<q``.
          ``q_sep1``, ``q_sep2``, ``G`` and ``b`` are determined from conditions
          of smoothness at the cross-overs.
  
      Literature:
      -----------
          B. Hammouda: A new Guinier-Porod model. J. Appl. Crystallogr. (2010) 43,
              716-719.