“…The motivation for the choice of the potential 1 + x 2 + y 2 + z 2 /q comes from the interest of this potential in galactic dynamics, see for instance [2,3,5,6,7,9,12,13,14,15,16]. The parameter q gives the ellipticity of the potential, which ranges in the interval √ 0.6 ≤ q ≤ 1.…”