sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
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use crate::pnp::{c2ixys, s00};

///  Form the celestial to intermediate-frame-of-date matrix for a given
///  date when the CIP X,Y coordinates are known.  IAU 2000.
///
///  Given:
///     date1,date2 f64          TT as a 2-part Julian Date (Note 1)
///     x,y         f64          Celestial Intermediate Pole (Note 2)
///
///  Returned (function value):
///                 [[f64; 3]; 3] celestial-to-intermediate matrix (Note 3)
///
///  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 Celestial Intermediate Pole coordinates are the x,y components
///     of the unit vector in the Geocentric Celestial Reference System.
///
///  3) The matrix rc2i is the first stage in the transformation from
///     celestial to terrestrial coordinates:
///
///        [TRS] = RPOM * R_3(ERA) * rc2i * [CRS]
///
///              = RC2T * [CRS]
///
///     where [CRS] is a vector in the Geocentric Celestial Reference
///     System and [TRS] is a vector in the International Terrestrial
///     Reference System (see IERS Conventions 2003), ERA is the Earth
///     Rotation Angle and RPOM is the polar motion matrix.
///
///  4) Although its name does not include "00", This function is in fact
///     specific to the IAU 2000 models.
///
///  Called:
///     iauC2ixys    celestial-to-intermediate matrix, given X,Y and s
///     iauS00       the CIO locator s, given X,Y, IAU 2000A
///
///  Reference:
///
///     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
///     IERS Technical Note No. 32, BKG (2004)
pub fn c2ixy(date1: f64, date2: f64, x: f64, y: f64) -> [[f64; 3]; 3] {
    /* Compute s and then the matrix. */
    c2ixys(x, y, s00(date1, date2, x, y))
}