rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use crate::vector_matrix::spherical_cartesian::{c2s::*, s2c::*};
use crate::vector_matrix::{angle_ops::{anp::*, anpm::*}, matrix_vec_prod::rxp};
use super::ecm06::*;
///  Transformation from ICRS equatorial coordinates to ecliptic
///  coordinates (mean equinox and ecliptic of date) using IAU 2006
///  precession model.
///
///  Given:
///    * date1,date2 TT as a 2-part Julian date (Note 1)
///    * dr,dd       ICRS right ascension and declination (radians)
///
///  Returned:
///     dl,db       ecliptic longitude and latitude (radians)
///
///  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) No assumptions are made about whether the coordinates represent
///     starlight and embody astrometric effects such as parallax or
///     aberration.
///
///  3) The transformation is approximately that from mean J2000.0 right
///     ascension and declination to ecliptic longitude and latitude
///     (mean equinox and ecliptic of date), with only frame bias (always
///     less than 25 mas) to disturb this classical picture.
///
///  Called:
///     eraS2c       spherical coordinates to unit vector
///     eraEcm06     J2000.0 to ecliptic rotation matrix, IAU 2006
///     eraRxp       product of r-matrix and p-vector
///     eraC2s       unit vector to spherical coordinates
///     eraAnp       normalize angle into range 0 to 2pi
///     eraAnpm      normalize angle into range +/- pi
///
///  This revision:  2021 May 11
pub fn eqec06(date1: f64, date2: f64, dr: f64, dd: f64, dl:&mut f64, db:&mut f64)
{
    /* Spherical to Cartesian. */
       let mut v1 = [0.; 3];
       s2c(dr, dd, &mut v1);
    
    /* Rotation matrix, ICRS equatorial to ecliptic. */
    let mut rm = [[0.0; 3]; 3];
       ecm06(date1, date2, &mut rm);
    
    /* The transformation from ICRS to ecliptic. */
    let mut v2 = [0.; 3];
       rxp(&rm, &v1, &mut v2);
    
    /* Cartesian to spherical. */
    let mut a =0.; let mut b = 0.;
       c2s(&v2, &mut a, &mut b);
    
    /* Express in conventional ranges. */
       *dl = anp(a);
       *db = anpm(b);
    
    /* Finished. */
}