rfa 0.5.9

use crate::rfam::*;
use super::prec76::prec76;
use crate::vector_matrix::{ init::ir::*, copy_ext::*};
use crate::vector_matrix::build_rotations::{rz::*, ry::*};

///  Precession matrix from J2000.0 to a specified date, IAU 1976 model.
///
///  Given:
///     date1,date2 double       ending date, TT (Note 1)
///
///  Returned:
///     rmatp       double[3][3] precession matrix, J2000.0 -> date1+date2
///
///  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
///
///         2450123.7           0.0       (JD method)
///         2451545.0       -1421.3       (J2000 method)
///         2400000.5       50123.2       (MJD method)
///         2450123.5           0.2       (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 operates in the sense V(date) = RMATP * V(J2000),
///     where the p-vector V(J2000) is with respect to the mean
///     equatorial triad of epoch J2000.0 and the p-vector V(date)
///     is with respect to the mean equatorial triad of the given
///     date.
///
///  3) Though the matrix method itself is rigorous, the precession
///     angles are expressed through canonical polynomials which are
///     valid only for a limited time span.  In addition, the IAU 1976
///     precession rate is known to be imperfect.  The absolute accuracy
///     of the present formulation is better than 0.1 arcsec from
///     1960AD to 2040AD, better than 1 arcsec from 1640AD to 2360AD,
///     and remains below 3 arcsec for the whole of the period
///     500BC to 3000AD.  The errors exceed 10 arcsec outside the
///     range 1200BC to 3900AD, exceed 100 arcsec outside 4200BC to
///     5600AD and exceed 1000 arcsec outside 6800BC to 8200AD.
///
///  Called:
///     eraPrec76    accumulated precession angles, IAU 1976
///     eraIr        initialize r-matrix to identity
///     eraRz        rotate around Z-axis
///     eraRy        rotate around Y-axis
///     eraCr        copy r-matrix
///
///  References:
///
///     Lieske, J.H., 1979, Astron.Astrophys. 73, 282.
///      equations (6) & (7), p283.
///
///     Kaplan,G.H., 1981. USNO circular no. 163, pA2.
///
///  This revision:  2021 May 11
pub fn pmat76(date1: f64, date2: f64, rmatp: &mut [[f64; 3];3])
{
   let mut zeta =0.0; let mut z =0.0; let mut theta =0.0;
   let mut wmat = [[0.0;3] ;3];


/* Precession Euler angles, J2000.0 to specified date. */
   prec76(URSA_DJ00, 0.0, date1, date2, &mut zeta, &mut z, &mut theta);

/* Form the rotation matrix. */
   ir(  &mut wmat);
   rz( -zeta, &mut wmat);
   ry(  theta, &mut wmat);
   rz( -z, &mut wmat);
   cr( &wmat, rmatp);

/* Finished. */

}