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# c2ixys

erfa.c2ixys(x, y, s)

  Form the celestial to intermediate-frame-of-date matrix given the CIP X,Y and the CIO locator s.

  Parameters
    x double array
    y double array
    s double array
  Returns
    rc2i double array

  Notes

  Wraps ERFA function `eraC2ixys`. The ERFA documentation is:

      - - - - - - - - - -
       e r a C 2 i x y s
      - - - - - - - - - -

      Form the celestial to intermediate-frame-of-date matrix given the CIP
      X,Y and the CIO locator s.

      Given:
         x,y      double         Celestial Intermediate Pole (Note 1)
         s        double         the CIO locator s (Note 2)

      Returned:
         rc2i     double[3][3]   celestial-to-intermediate matrix (Note 3)

      Notes:

      1) The Celestial Intermediate Pole coordinates are the x,y
         components of the unit vector in the Geocentric Celestial
         Reference System.

      2) The CIO locator s (in radians) positions the Celestial
         Intermediate Origin on the equator of the CIP.

      3) The matrix rc2i is the first stage in the transformation from
         celestial to terrestrial coordinates:

            [TRS] = RPOM * R_3(ERA) * rc2i * [CRS]

                  = RC2T * [CRS]

         where [CRS] is a vector in the Geocentric Celestial Reference
         System and [TRS] is a vector in the International Terrestrial
         Reference System (see IERS Conventions 2003), ERA is the Earth
         Rotation Angle and RPOM is the polar motion matrix.

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