sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
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use super::{fw2m, nut06a, pfw06};

///  Classical NPB matrix, IAU 2006/2000A
///
///  Form the matrix of precession-nutation for a given date (including
///  frame bias), equinox based, IAU 2006 precession and IAU 2000A
///  nutation models.
///
///  This function is part of the International Astronomical Union's
///  SOFA (Standards of Fundamental Astronomy) software collection.
///
///  Status:  support function.
///
///  Given:
///  ```
///     date1,date2 double       TT as a 2-part Julian Date (Note 1)
///  ```
///  Returned:
///  ```
///     rbpn        double[3][3] bias-precession-nutation matrix (Note 2)
///  ```
///  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) = rbpn * V(GCRS), where
///     the p-vector V(date) is with respect to the true equatorial triad
///     of date date1+date2 and the p-vector V(GCRS) is with respect to
///     the Geocentric Celestial Reference System (IAU, 2000).
///
///  Called:
///     iauPfw06     bias-precession F-W angles, IAU 2006
///     iauNut06a    nutation, IAU 2006/2000A
///     iauFw2m      F-W angles to r-matrix
///
///  Reference:
///
///     Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855.
pub fn pnm06a(date1: f64, date2: f64) -> [[f64; 3]; 3] {
    /* Fukushima-Williams angles for frame bias and precession. */
    let (gamb, phib, psib, epsa) = pfw06(date1, date2);

    /* Nutation components. */
    let (dp, de) = nut06a(date1, date2);

    /* Equinox based nutation x precession x bias matrix. */
    fw2m(gamb, phib, psib + dp, epsa + de)
}