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# ltecm

erfa.ltecm(epj)

  ICRS equatorial to ecliptic rotation matrix, long-term.

  Parameters
    epj double array
  Returns
    rm double array

  Notes

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

      - - - - - - - - -
       e r a L t e c m
      - - - - - - - - -

      ICRS equatorial to ecliptic rotation matrix, long-term.

      Given:
         epj     double         Julian epoch (TT)

      Returned:
         rm      double[3][3]   ICRS to ecliptic rotation matrix

      Notes:

      1) The matrix is in the sense

            E_ep = rm x P_ICRS,

         where P_ICRS is a vector with respect to ICRS right ascension
         and declination axes and E_ep is the same vector with respect to
         the (inertial) ecliptic and equinox of epoch epj.

      2) P_ICRS is a free vector, merely a direction, typically of unit
         magnitude, and not bound to any particular spatial origin, such
         as the Earth, Sun or SSB.  No assumptions are made about whether
         it represents starlight and embodies astrometric effects such as
         parallax or aberration.  The transformation is approximately that
         between mean J2000.0 right ascension and declination and ecliptic
         longitude and latitude, with only frame bias (always less than
         25 mas) to disturb this classical picture.

      3) The Vondrak et al. (2011, 2012) 400 millennia precession model
         agrees with the IAU 2006 precession at J2000.0 and stays within
         100 microarcseconds during the 20th and 21st centuries.  It is
         accurate to a few arcseconds throughout the historical period,
         worsening to a few tenths of a degree at the end of the
         +/- 200,000 year time span.

      Called:
         eraLtpequ    equator pole, long term
         eraLtpecl    ecliptic pole, long term
         eraPxp       vector product
         eraPn        normalize vector

      References:

        Vondrak, J., Capitaine, N. and Wallace, P., 2011, New precession
        expressions, valid for long time intervals, Astron.Astrophys. 534,
        A22

        Vondrak, J., Capitaine, N. and Wallace, P., 2012, New precession
        expressions, valid for long time intervals (Corrigendum),
        Astron.Astrophys. 541, C1

      This revision:  2021 May 11

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