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# gst06

erfa.gst06(uta, utb, tta, ttb, rnpb)

  Greenwich apparent sidereal time, IAU 2006, given the NPB matrix.

  Parameters
    uta double array
    utb double array
    tta double array
    ttb double array
    rnpb double array
  Returns
    c_retval double array

  Notes

  Wraps ERFA function `eraGst06`. The ERFA documentation is:

      - - - - - - - - -
       e r a G s t 0 6
      - - - - - - - - -

      Greenwich apparent sidereal time, IAU 2006, given the NPB matrix.

      Given:
         uta,utb  double        UT1 as a 2-part Julian Date (Notes 1,2)
         tta,ttb  double        TT as a 2-part Julian Date (Notes 1,2)
         rnpb     double[3][3]  nutation x precession x bias matrix

      Returned (function value):
                  double        Greenwich apparent sidereal time (radians)

      Notes:

      1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
         Julian Dates, apportioned in any convenient way between the
         argument pairs.  For example, JD(UT1)=2450123.7 could be
         expressed in any of these ways, among others:

                 uta            utb

             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 (in the case of UT;  the TT is not at all critical
         in this respect).  The J2000 and MJD methods are good compromises
         between resolution and convenience.  For UT, the date & time
         method is best matched to the algorithm that is used by the Earth
         rotation angle function, called internally:  maximum precision is
         delivered when the uta argument is for 0hrs UT1 on the day in
         question and the utb argument lies in the range 0 to 1, or vice
         versa.

      2) Both UT1 and TT are required, UT1 to predict the Earth rotation
         and TT to predict the effects of precession-nutation.  If UT1 is
         used for both purposes, errors of order 100 microarcseconds
         result.

      3) Although the function uses the IAU 2006 series for s+XY/2, it is
         otherwise independent of the precession-nutation model and can in
         practice be used with any equinox-based NPB matrix.

      4) The result is returned in the range 0 to 2pi.

      Called:
         eraBpn2xy    extract CIP X,Y coordinates from NPB matrix
         eraS06       the CIO locator s, given X,Y, IAU 2006
         eraAnp       normalize angle into range 0 to 2pi
         eraEra00     Earth rotation angle, IAU 2000
         eraEors      equation of the origins, given NPB matrix and s

      Reference:

         Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981

      This revision:  2021 May 11

      Copyright (C) 2013-2021, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.