rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use crate::vector_matrix::angle_ops::anp::anp;
use crate::prec_nut::{bpn2xy::*, s06::*, eors::*};
use super::era00::*;
///  Greenwich apparent sidereal time, IAU 2006, given the NPB matrix.
///
///  Given:
///   *  uta,utb  UT1 as a 2-part Julian Date (Notes 1,2)
///   *  tta,ttb  TT as a 2-part Julian Date (Notes 1,2)
///   *  rnpb     nutation x precession x bias matrix
///
///  Returned (function value):
///              double        Greenwich apparent sidereal time (radians)
///
/// # Notes:
///
///  1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
///     Julian Dates, apportioned in any convenient way between the
///     argument pairs.  For example, JD(UT1)=2450123.7 could be
///     expressed in any of these ways, among others:
///
///     |    uta      |      utb     |                      |
///     |-------------|--------------|----------------------|
///     |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 (in the case of UT;  the TT is not at all critical
///     in this respect).  The J2000 and MJD methods are good compromises
///     between resolution and convenience.  For UT, the date & time
///     method is best matched to the algorithm that is used by the Earth
///     rotation angle function, called internally:  maximum precision is
///     delivered when the uta argument is for 0hrs UT1 on the day in
///     question and the utb argument lies in the range 0 to 1, or vice
///     versa.
///
///  2) Both UT1 and TT are required, UT1 to predict the Earth rotation
///     and TT to predict the effects of precession-nutation.  If UT1 is
///     used for both purposes, errors of order 100 microarcseconds
///     result.
///
///  3) Although the function uses the IAU 2006 series for s+XY/2, it is
///     otherwise independent of the precession-nutation model and can in
///     practice be used with any equinox-based NPB matrix.
///
///  4) The result is returned in the range 0 to 2pi.
///
/// # Called:
///   * bpn2xy    extract CIP X,Y coordinates from NPB matrix
///   * s06       the CIO locator s, given X,Y, IAU 2006
///   * anp       normalize angle into range 0 to 2pi
///   * era00     Earth rotation angle, IAU 2000
///   * eors      equation of the origins, given NPB matrix and s
///
/// # Reference:
///   * Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
///
///  This revision:  2021 May 11

pub fn gst06(uta: f64, utb: f64, tta: f64, ttb: f64,
    rnpb: &[[f64; 3];3])->f64
{
    let mut x =0.0; let mut y =0.0; 
 
 
 /* Extract CIP coordinates. */
    bpn2xy(&rnpb, &mut x, &mut y);
 
 /* The CIO locator, s. */
    let s = s06(tta, ttb, x, y);
 
 /* Greenwich apparent sidereal time. */
    let era = era00(uta, utb);
    let eors = eors(&rnpb, s);
    anp(era - eors)
 
 /* Finished. */
 
 }