Function pnm06a 

pub fn pnm06a(date1: f64, date2: f64) -> [[f64; 3]; 3]

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.