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