The precession-nutation models based on the IAU 2000A nutation series involve several thousand amplitude coefficients, many under 1μas in size, and the sines and cosines of about 1350 angles. For the many applications that do not require the utmost accuracy this represents an unnecessary or even excessive computational overhead. The IAU 2000B model offers one alternative, an order of magnitude smaller than IAU 2000A and delivering classical nutation components of 1 mas accuracy in the current era. In a recent paper (Capitaine & Wallace 2007), the main results of which are provided here, we looked at other options, based on series for the CIP coordinates and the CIO locator and with the GCRS to CIRS rotation matrix as the end product. Truncation of the series provides most of the savings, but certain other measures can be taken also. Three example formulations are presented that achieve 1 mas, 16 mas and 0.4 arcsec accuracy throughout 1995-2050 with computational costs 1, 2 and 3 orders of magnitude less than the full models. A few examples of possible applications are presented.
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