<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def shepp_logan_ellipsoids(ndim, modified=False):
 """Ellipsoids for the standard Shepp-Logan phantom in 2 or 3 dimensions. Parameters ndim : {2, 3} Dimension of the space the ellipsoids should be in. modified : bool, optional True if the modified Shepp-Logan phantom should be given. The modified phantom has greatly amplified contrast to aid visualization. See Also -------- odl.phantom.geometric.ellipsoid_phantom : Function for creating arbitrary ellipsoids phantoms shepp_logan : Create a phantom with these ellipsoids References .. _Shepp-Logan phantom: https://en.wikipedia.org/wiki/Shepp-Logan_phantom """

    if ndim == 2:
        ellipsoids = _shepp_logan_ellipse_2d()
    elif ndim == 3:
        ellipsoids = _shepp_logan_ellipsoids_3d()
    else:
        raise ValueError('dimension not 2 or 3, no phantom available')

    if modified:
        _modified_shepp_logan_ellipsoids(ellipsoids)

    return ellipsoids