SLA_PRENUT - Precession-Nutation Matrix

ACTION:

Form the matrix of precession and nutation (SF2001).

CALL:

CALL sla_PRENUT (EPOCH, DATE, RMATPN)

GIVEN:

EPOCH	D	Julian Epoch for mean coordinates
DATE	D	Modified Julian Date (JD$-$2400000.5) for true coordinates

RETURNED:

RMATPN

D(3,3)

combined precession-nutation matrix

NOTES:

1. The epoch and date are TDB. TT (or even UTC) will do.
2. The matrix is in the sense:

   v$_{true}$ = M$\cdot$v$_{mean}$

   where v$_{true}$ is the star vector relative to the true equator and equinox of epoch DATE, M is the $3\times3$ matrix RMATPN and v$_{mean}$ is the star vector relative to the mean equator and equinox of epoch EPOCH.