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# pom00

erfa.pom00(xp, yp, sp)

  Form the matrix of polar motion for a given date, IAU 2000.

  Parameters
    xp double array
    yp double array
    sp double array
  Returns
    rpom double array

  Notes

  Wraps ERFA function `eraPom00`. The ERFA documentation is:

      - - - - - - - - - -
       e r a P o m 0 0
      - - - - - - - - - -

      Form the matrix of polar motion for a given date, IAU 2000.

      Given:
         xp,yp    double    coordinates of the pole (radians, Note 1)
         sp       double    the TIO locator s' (radians, Note 2)

      Returned:
         rpom     double[3][3]   polar-motion matrix (Note 3)

      Notes:

      1) The arguments xp and yp are the coordinates (in radians) of the
         Celestial Intermediate Pole with respect to the International
         Terrestrial Reference System (see IERS Conventions 2003),
         measured along the meridians 0 and 90 deg west respectively.

      2) The argument sp is the TIO locator s', in radians, which
         positions the Terrestrial Intermediate Origin on the equator.  It
         is obtained from polar motion observations by numerical
         integration, and so is in essence unpredictable.  However, it is
         dominated by a secular drift of about 47 microarcseconds per
         century, and so can be taken into account by using s' = -47*t,
         where t is centuries since J2000.0.  The function eraSp00
         implements this approximation.

      3) The matrix operates in the sense V(TRS) = rpom * V(CIP), meaning
         that it is the final rotation when computing the pointing
         direction to a celestial source.

      Called:
         eraIr        initialize r-matrix to identity
         eraRz        rotate around Z-axis
         eraRy        rotate around Y-axis
         eraRx        rotate around X-axis

      Reference:

         McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
         IERS Technical Note No. 32, BKG (2004)

      This revision:  2021 May 11

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