<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def GuinierPorod(q, G, Rg, alpha):
 """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. """

    return GuinierPorodMulti(q, G, Rg, alpha)