ecmat.f

      SUBROUTINE sla_ECMAT (DATE, RMAT)
*+
*     - - - - - -
*      E C M A T
*     - - - - - -
*
*  Form the equatorial to ecliptic rotation matrix - IAU 1980 theory
*  (double precision)
*
*  Given:
*     DATE     dp         TDB (loosely ET) as Modified Julian Date
*                                            (JD-2400000.5)
*  Returned:
*     RMAT     dp(3,3)    matrix
*
*  Reference:
*     Murray,C.A., Vectorial Astrometry, section 4.3.
*
*  Note:
*    The matrix is in the sense   V(ecl)  =  RMAT * V(equ);  the
*    equator, equinox and ecliptic are mean of date.
*
*  Called:  sla_DEULER
*
*  P.T.Wallace   Starlink   23 August 1996
*
*  Copyright (C) 1996 Rutherford Appleton Laboratory
*
*  License:
*    This program is free software; you can redistribute it and/or modify
*    it under the terms of the GNU General Public License as published by
*    the Free Software Foundation; either version 2 of the License, or
*    (at your option) any later version.
*
*    This program is distributed in the hope that it will be useful,
*    but WITHOUT ANY WARRANTY; without even the implied warranty of
*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*    GNU General Public License for more details.
*
*    You should have received a copy of the GNU General Public License
*    along with this program (see SLA_CONDITIONS); if not, write to the 
*    Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
*    Boston, MA  02111-1307  USA
*
*-

      IMPLICIT NONE

      DOUBLE PRECISION DATE,RMAT(3,3)

*  Arc seconds to radians
      DOUBLE PRECISION AS2R
      PARAMETER (AS2R=0.484813681109535994D-5)

      DOUBLE PRECISION T,EPS0



*  Interval between basic epoch J2000.0 and current epoch (JC)
      T = (DATE-51544.5D0)/36525D0

*  Mean obliquity
      EPS0 = AS2R*
     :   (84381.448D0+(-46.8150D0+(-0.00059D0+0.001813D0*T)*T)*T)

*  Matrix
      CALL sla_DEULER('X',EPS0,0D0,0D0,RMAT)

      END