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slalib/ecmat.f

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+      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