<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def defrise_ellipses(ndim, nellipses=8, alternating=False):
 """Ellipses for the standard Defrise phantom in 2 or 3 dimensions. Parameters ndim : {2, 3} Dimension of the space for the ellipses/ellipsoids. nellipses : int, optional Number of ellipses. If more ellipses are used, each ellipse becomes thinner. alternating : bool, optional True if the ellipses should have alternating densities (+1, -1), otherwise all ellipses have value +1. See Also -------- odl.phantom.geometric.ellipsoid_phantom : Function for creating arbitrary ellipsoids phantoms odl.phantom.transmission.shepp_logan_ellipsoids """

    ellipses = []
    if ndim == 2:
        for i in range(nellipses):
            if alternating:
                value = (-1.0 + 2.0 * (i % 2))
            else:
                value = 1.0

            axis_1 = 0.5
            axis_2 = 0.5 / (nellipses + 1)
            center_x = 0.0
            center_y = -1 + 2.0 / (nellipses + 1.0) * (i + 1)
            rotation = 0
            ellipses.append(
                [value, axis_1, axis_2, center_x, center_y, rotation])
    elif ndim == 3:
        for i in range(nellipses):
            if alternating:
                value = (-1.0 + 2.0 * (i % 2))
            else:
                value = 1.0

            axis_1 = axis_2 = 0.5
            axis_3 = 0.5 / (nellipses + 1)
            center_x = center_y = 0.0
            center_z = -1 + 2.0 / (nellipses + 1.0) * (i + 1)
            rotation_phi = rotation_theta = rotation_psi = 0

            ellipses.append(
                [value, axis_1, axis_2, axis_3,
                 center_x, center_y, center_z,
                 rotation_phi, rotation_theta, rotation_psi])

    return ellipses