rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use crate::rfam::*;
use super::obl06::*;
///  Precession angles, IAU 2006 (Fukushima-Williams 4-angle formulation).
///
///  Given:
///     date1,date2  double   TT as a 2-part Julian Date (Note 1)
///
///  Returned:
///     gamb         double   F-W angle gamma_bar (radians)
///     phib         double   F-W angle phi_bar (radians)
///     psib         double   F-W angle psi_bar (radians)
///     epsa         double   F-W angle epsilon_A (radians)
///
///  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) Naming the following points:
///
///           e = J2000.0 ecliptic pole,
///           p = GCRS pole,
///           E = mean ecliptic pole of date,
///     and   P = mean pole of date,
///
///     the four Fukushima-Williams angles are as follows:
///
///        gamb = gamma_bar = epE
///        phib = phi_bar = pE
///        psib = psi_bar = pEP
///        epsa = epsilon_A = EP
///
///  3) The matrix representing the combined effects of frame bias and
///     precession is:
///
///        PxB = R_1(-epsa).R_3(-psib).R_1(phib).R_3(gamb)
///
///  4) The matrix representing the combined effects of frame bias,
///     precession and nutation is simply:
///
///        NxPxB = R_1(-epsa-dE).R_3(-psib-dP).R_1(phib).R_3(gamb)
///
///     where dP and dE are the nutation components with respect to the
///     ecliptic of date.
///
///  Reference:
///
///     Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351
///
///  Called:
///     eraObl06     mean obliquity, IAU 2006
///
///  This revision:  2021 May 11
pub fn pfw06(date1: f64, date2: f64,
    gamb: &mut f64, phib: &mut f64, psib: &mut f64, epsa: &mut f64)
{
 /* Interval between fundamental date J2000.0 and given date (JC). */
    let t = ((date1 - URSA_DJ00) + date2) / URSA_DJC;
 
 /* P03 bias+precession angles. */
    *gamb = (    -0.052928     +
            (    10.556378     +
            (     0.4932044    +
            (    -0.00031238   +
            (    -0.000002788  +
            (     0.0000000260 )
            * t) * t) * t) * t) * t) * URSA_DAS2R;
    *phib = ( 84381.412819     +
            (   -46.811016     +
            (     0.0511268    +
            (     0.00053289   +
            (    -0.000000440  +
            (    -0.0000000176 )
            * t) * t) * t) * t) * t) * URSA_DAS2R;
    *psib = (    -0.041775     +
            (  5038.481484     +
            (     1.5584175    +
            (    -0.00018522   +
            (    -0.000026452  +
            (    -0.0000000148 )
            * t) * t) * t) * t) * t) * URSA_DAS2R;
    *epsa =  obl06(date1, date2);
 
 /* Finished. */
 
 }