rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use super::{nutm80::*, pmat76::*, };
use crate::vector_matrix::matrix_ops::rxr::rxr;
///  Form the matrix of precession/nutation for a given date, IAU 1976
///  precession model, IAU 1980 nutation model.
///
///  Given:
///     date1,date2 double       TT as a 2-part Julian Date (Note 1)
///
///  Returned:
///     rmatpn         double[3][3]   combined precession/nutation matrix
///
///  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) = rmatpn * V(J2000),
///     where the p-vector V(date) is with respect to the true equatorial
///     triad of date date1+date2 and the p-vector V(J2000) is with
///     respect to the mean equatorial triad of epoch J2000.0.
///
///  Called:
///     eraPmat76    precession matrix, IAU 1976
///     eraNutm80    nutation matrix, IAU 1980
///     eraRxr       product of two r-matrices
///
///  Reference:
///
///     Explanatory Supplement to the Astronomical Almanac,
///     P. Kenneth Seidelmann (ed), University Science Books (1992),
///     Section 3.3 (p145).
///
///  This revision:  2021 May 11
pub fn pnm80(date1: f64, date2: f64, rmatpn: &mut [[f64; 3];3])
{
    let mut rmatp = [[0.0; 3]; 3]; let mut rmatn = [[0.0; 3]; 3];
 
 
 /* Precession matrix, J2000.0 to date. */
    pmat76(date1, date2, &mut rmatp);
 
 /* Nutation matrix. */
    nutm80(date1, date2, &mut rmatn);
 
 /* Combine the matrices:  PN = N x P. */
    rxr(&rmatn, &rmatp, rmatpn);
 
 /* Finished. */
 
 }