[SOFA] Returns the frame bias components of the IAU 2000
precession-nutation models (part of MHB2000 with additions), in a
double array. The elements are: (0) the longitude
correction in radians, (1) the obliquity correction in radians, (2)
the ICRS right ascension of the J2000.0 mean equinox in radians.
The frame bias corrections in longitude and obliquity define a J2000.0 mean pole in Geocentric Celestial Reference System coordinates, consistent with the rest of the IAU 2000A precession-nutation model. The right ascension correction is not part of the IAU 2000A model but is due to Chapront et al. (2002) Astron. Astrophys., 387, 700.
See also: bp00, bp06