code: def GuinierPorodGuinier(q, G, Rg1, alpha, Rg2):
      
      return GuinierPorodMulti(q, G, Rg1, alpha, Rg2)
docs: Empirical Guinier-Porod-Guinier scattering
  
      Inputs:
      -------
          ``q``: independent variable
          ``G``: factor for the first Guinier-branch
          ``Rg1``: the first radius of gyration
          ``alpha``: the power-law exponent
          ``Rg2``: the second radius of gyration
  
      Formula:
      --------
          ``G*exp(-q^2*Rg1^2/3)`` if ``q<q_sep1``.
          ``A*q^alpha`` if ``q_sep1 <= q  <=q_sep2``.
          ``G2*exp(-q^2*Rg2^2/3)`` if ``q_sep2<q``.
          The parameters ``A``,``G2``, ``q_sep1``, ``q_sep2`` 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.