$LastChangedDate: 27-Juil-2011 $

# CL_mod_precessionMatrix

Precession matrix and rotation vectors (IERS 1996)

## Calling Sequence

       [PREC[,OM[,OMP]]] = CL_mod_precessionMatrix(K,KP,KPP[,flag])

## Description

- Computes the precession matrix, rotation vector and its time derivatives.

  Matrix from mean equator/equinox at date t to mean equator/equinox at J2000.

  if P0 is the pole of J2000 equator, and P is the pole of the equator at date t; if G0 is the equinox of J2000 and G is the equinox at date t:

  zetaa : angle between the meridians (pole P0) P0-P and P0-G0

  thetaa: angle between the equateur J2000 and the equateur t

  za : angle between the meridians (pole P) P-P0 and P-G

## Parameters

K :

  [zetaa;tetaa;za] (3xN)

KP :

  [zetaap;tetaap;zap] (3xN)

KPP :

  [zetaapp;tetaapp;zapp] (3xN)

flag :

  (optional) "n" -> matrix only; "p" -> matrix and rotation vector; "s" -> matrix, rotation vector and its time derivatives (defatul depends on number of outputs)

PREC:

  precession matrix (3x3xN)

OM:

  (optional) rotation vectors (3xN)

OMP:

  (optional) first time derivative of OM (3xN)

## Authors

- CNES - DCT/SB

## Bibliography

- 1) IERS Conventions (1996), Dennis D. McCarthy

- 2) Explanatory Supplement to the Astronomical Almanac, Seidelman (1992)

## See also

- CL_mod_precessionAngles

- CL_rot_angles2matrix

- CL_rot_angularVelocity

## Examples

    jj_tai = [19500:1:20500];
    ss_tai = 43200*ones(jj_tai);
    [K,KP,KPP]=CL_mod_precessionAngles(jj_tai,ss_tai,"s");
    [PREC,OM,OMP] = CL_mod_precessionMatrix(K,KP,KPP,"s");