update ast 8.6.2

1 files changed, 107 insertions, 0 deletions

diff --git a/ast/pal/palPrec.c b/ast/pal/palPrec.c
new file mode 100644
index 0000000..678770d
--- /dev/null
+++ b/ast/pal/palPrec.c
@@ -0,0 +1,107 @@
+/*
+*+
+*  Name:
+*     palPrec
+
+*  Purpose:
+*     Form the matrix of precession between two epochs (IAU 2006)
+
+*  Language:
+*     Starlink ANSI C
+
+*  Type of Module:
+*     Library routine
+
+*  Invocation:
+*     palPrec( double ep0, double ep1, double rmatp[3][3] )
+
+*  Arguments:
+*     ep0 = double (Given)
+*        Beginning epoch
+*     ep1 = double (Given)
+*        Ending epoch
+*     rmatp = double[3][3] (Returned)
+*        Precession matrix
+
+*  Description:
+*     The IAU 2006 precession matrix from ep0 to ep1 is found and
+*     returned. The matrix is in the sense  V(EP1)  =  RMATP * V(EP0).
+*     The epochs are TDB (loosely TT) Julian epochs.
+*
+*     Though the matrix method itself is rigorous, the precession
+*     angles are expressed through canonical polynomials which are
+*     valid only for a limited time span of a few hundred years around
+*     the current epoch.
+
+*  Authors:
+*     PTW: Pat Wallace (STFC)
+*     DSB: David Berry (JAC, Hawaii)
+*     {enter_new_authors_here}
+
+*  History:
+*     2012-02-10 (DSB):
+*        Initial version with documentation taken from Fortran SLA
+*        Adapted with permission from the Fortran SLALIB library.
+*     {enter_further_changes_here}
+
+*  Copyright:
+*     Copyright (C) 1996 Rutherford Appleton Laboratory
+*     Copyright (C) 2012 Science and Technology Facilities Council.
+*     All Rights Reserved.
+
+*  Licence:
+*     This program is free software: you can redistribute it and/or
+*     modify it under the terms of the GNU Lesser General Public
+*     License as published by the Free Software Foundation, either
+*     version 3 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 Lesser General Public License for more details.
+*
+*     You should have received a copy of the GNU Lesser General
+*     License along with this program.  If not, see
+*     <http://www.gnu.org/licenses/>.
+
+*  Bugs:
+*     {note_any_bugs_here}
+*-
+*/
+
+#include "pal.h"
+#include "pal1sofa.h"
+
+void palPrec( double ep0, double ep1, double rmatp[3][3] ){
+
+/* Local Variables: */
+   double rmatq[3][3];
+   double ep0_days;
+   double ep1_days;
+
+/* Convert supplied dates to days since J2000 */
+   ep0_days = ( ep0 - 2000.0 )*ERFA_DJY;
+   ep1_days = ( ep1 - 2000.0 )*ERFA_DJY;
+
+/* If beginning epoch is J2000, just return the rotation matrix from
+   J2000 to EP1. */
+   if( ep0 == 2000.0 ) {
+      eraPmat06( ERFA_DJ00, ep1_days, rmatp );
+
+/* If end epoch is J2000, get the rotation matrix from J2000 to EP0 and
+   then transpose it to get the rotation matrix from EP0 to J2000. */
+   } else if( ep1 == 2000.0 ) {
+      eraPmat06( ERFA_DJ00, ep0_days, rmatp );
+      eraTr( rmatp, rmatp );
+
+/* Otherwise. get the two matrices used above and multiply them
+   together. */
+   } else {
+      eraPmat06( ERFA_DJ00, ep0_days, rmatp );
+      eraTr( rmatp, rmatp );
+      eraPmat06( ERFA_DJ00, ep1_days, rmatq );
+      eraRxr( rmatp, rmatq, rmatp );
+   }
+
+}