SUBROUTINE iau_C2IBPN ( DATE1, DATE2, RBPN, RC2I )
*+
*  - - - - - - - - - - -
*   i a u _ C 2 I B P N
*  - - - - - - - - - - -
*
*  Form the celestial-to-intermediate matrix for a given date given
*  the bias-precession-nutation matrix.  IAU 2000.
*
*  This routine is part of the International Astronomical Union's
*  SOFA (Standards of Fundamental Astronomy) software collection.
*
*  Status:  support routine.
*
*  Given:
*     DATE1,DATE2    d       TT as a 2-part Julian Date (Note 1)
*     RBPN         d(3,3)    celestial-to-true matrix (Note 2)
*
*  Returned:
*     RC2I         d(3,3)    celestial-to-intermediate matrix (Note 3)
*
*  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
*
*         2450123.7D0        0D0        (JD method)
*          2451545D0      -1421.3D0     (J2000 method)
*         2400000.5D0     50123.2D0     (MJD method)
*         2450123.5D0       0.2D0       (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 RBPN transforms vectors from GCRS to true equator (and
*     CIO or equinox) of date.  Only the CIP (bottom row) is used.
*
*  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.
*
*  4) Although its name does not include "00", this routine is in fact
*     specific to the IAU 2000 models.
*
*  Called:
*     iau_BPN2XY   extract CIP X,Y coordinates from NPB matrix
*     iau_C2IXY    celestial-to-intermediate matrix, given X,Y
*
*  References:
*
*     Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
*     "Expressions for the Celestial Intermediate Pole and Celestial
*     Ephemeris Origin consistent with the IAU 2000A precession-nutation
*     model", Astronomy & Astrophysics, 400, 1145-1154 (2003)
*
*     n.b. The celestial ephemeris origin (CEO) was renamed "celestial
*          intermediate origin" (CIO) by IAU 2006 Resolution 2.
*
*     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
*     IERS Technical Note No. 32, BKG (2004)
*
*  This revision:  2007 June 1
*
*  Copyright (C) 2008 IAU SOFA Review Board.  See notes at end.
*
*-----------------------------------------------------------------------

      IMPLICIT NONE

      DOUBLE PRECISION DATE1, DATE2, RBPN(3,3), RC2I(3,3)

      DOUBLE PRECISION X, Y

* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

*  Extract the X,Y coordinates.
      CALL iau_BPN2XY ( RBPN, X, Y )

*  Form the celestial-to-intermediate matrix (n.b. IAU 2000 specific).
      CALL iau_C2IXY ( DATE1, DATE2, X, Y, RC2I )

*  Finished.

*+-----------------------------------------------------------------------
*
*  Copyright (C) 2008
*  Standards Of Fundamental Astronomy Review Board
*  of the International Astronomical Union.
*
*  =====================
*  SOFA Software License
*  =====================
*
*  NOTICE TO USER:
*
*  BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING TERMS AND CONDITIONS
*  WHICH APPLY TO ITS USE.
*
*  1. The Software is owned by the IAU SOFA Review Board ("the Board").
*
*  2. Permission is granted to anyone to use the SOFA software for any
*     purpose, including commercial applications, free of charge and
*     without payment of royalties, subject to the conditions and 
*     restrictions listed below.
*
*  3. You (the user) may copy and adapt the SOFA software and its 
*     algorithms for your own purposes and you may copy and distribute
*     a resulting "derived work" to others on a world-wide, royalty-free 
*     basis, provided that the derived work complies with the following
*     requirements: 
*
*     a) Your work shall be marked or carry a statement that it (i) uses
*        routines and computations derived by you from software provided 
*        by SOFA under license to you; and (ii) does not contain
*        software provided by SOFA or software that has been distributed
*        by or endorsed by SOFA.
*
*     b) The source code of your derived work must contain descriptions
*        of how the derived work is based upon and/or differs from the
*        original SOFA software.
*
*     c) The name(s) of all routine(s) that you distribute shall differ
*        from the SOFA names, even when the SOFA content has not been
*        otherwise changed.
*
*     d) The routine-naming prefix "iau" shall not be used.
*
*     e) The origin of the SOFA components of your derived work must not
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*        original software, nor file a patent application for SOFA
*        software or algorithms embedded in the SOFA software.
*
*     f) These requirements must be reproduced intact in any source
*        distribution and shall apply to anyone to whom you have granted 
*        a further right to modify the source code of your derived work.
*
*  4. In any published work or commercial products which includes
*     results achieved by using the SOFA software, you shall acknowledge
*     that the SOFA software was used in obtaining those results.
*
*  5. You shall not cause the SOFA software to be brought into
*     disrepute, either by misuse, or use for inappropriate tasks, or by
*     inappropriate modification.
*
*  6. The SOFA software is provided "as is" and the Board makes no 
*     warranty as to its use or performance.   The Board does not and 
*     cannot warrant the performance or results which the user may obtain 
*     by using the SOFA software.  The Board makes no warranties, express 
*     or implied, as to non-infringement of third party rights,
*     merchantability, or fitness for any particular purpose.  In no
*     event will the Board be liable to the user for any consequential,
*     incidental, or special damages, including any lost profits or lost
*     savings, even if a Board representative has been advised of such
*     damages, or for any claim by any third party.
*
*  7. The provision of any version of the SOFA software under the terms 
*     and conditions specified herein does not imply that future
*     versions will also be made available under the same terms and
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*
*  Correspondence concerning SOFA software should be addressed as
*  follows:
*
*     Internet email: sofa@rl.ac.uk
*     Postal address: IAU SOFA Center
*                     Rutherford Appleton Laboratory
*                     Chilton, Didcot, Oxon OX11 0QX
*                     United Kingdom
*
*-----------------------------------------------------------------------

      END