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# pnm00b

erfa.pnm00b(date1, date2)

  Form the matrix of precession-nutation for a given date (including frame bias), equinox-based, IAU 2000B model.

  Parameters:
    date1 double array
    date2 double array
  Returns:
    rbpn double array

  Notes

  Wraps ERFA function `eraPnm00b`. The ERFA documentation is:

      - - - - - - - - - -
       e r a P n m 0 0 b
      - - - - - - - - - -

      Form the matrix of precession-nutation for a given date (including
      frame bias), equinox-based, IAU 2000B model.

      Given:
         date1,date2 double       TT as a 2-part Julian Date (Note 1)

      Returned:
         rbpn        double[3][3] bias-precession-nutation matrix (Note 2)

      Notes:

      1) The TT date date1+date2 is a Julian Date, apportioned in any
         convenient way between the two arguments.  For example,
         JD(TT)=2450123.7 could be expressed in any of these ways, among
         others:

                date1          date2

             2450123.7           0.0       (JD method)
             2451545.0       -1421.3       (J2000 method)
             2400000.5       50123.2       (MJD method)
             2450123.5           0.2       (date & time method)

         The JD method is the most natural and convenient to use in
         cases where the loss of several decimal digits of resolution
         is acceptable.  The J2000 method is best matched to the way
         the argument is handled internally and will deliver the
         optimum resolution.  The MJD method and the date & time methods
         are both good compromises between resolution and convenience.

      2) The matrix operates in the sense V(date) = rbpn * V(GCRS), where
         the p-vector V(date) is with respect to the true equatorial triad
         of date date1+date2 and the p-vector V(GCRS) is with respect to
         the Geocentric Celestial Reference System (IAU, 2000).

      3) The present function is faster, but slightly less accurate (about
         1 mas), than the eraPnm00a function.

      Called:
         eraPn00b     bias/precession/nutation, IAU 2000B

      Reference:

         IAU: Trans. International Astronomical Union, Vol. XXIVB;  Proc.
         24th General Assembly, Manchester, UK.  Resolutions B1.3, B1.6.
         (2000)

      This revision:  2021 May 11

      Copyright (C) 2013-2023, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.