  According to the so-called "global polytropic model", hydrostatic equilibrium
for a planetary system leads to the Lane-Emden differential equation. Solving
this equation in the complex plane, we obtain polytropic spherical shells
defined by succesive roots of the real part $\mathrm{Re}(\theta)$ of the
Lane-Emden function $\theta$. Such shells provide hosting orbits for the
members of a planetary system. Within the framework of the global polytropic
model, we study the exoplanet systems HD 40307, $\mu$ Ara, Kepler-26,
Kepler-62, and Kepler-275. We give emphasis on comparing our results with
observations, and with orbit predictions derived from the "generalized
Titius-Bode relation".
