SUBROUTINE iau_FW2XY ( GAMB, PHIB, PSI, EPS, X, Y )
*+
* - - - - - - - - - -
* i a u _ F W 2 X Y
* - - - - - - - - - -
*
* CIP X,Y given Fukushima-Williams bias-precession-nutation angles.
*
* This routine is part of the International Astronomical Union's
* SOFA (Standards of Fundamental Astronomy) software collection.
*
* Status: support routine.
*
* Given:
* GAMB d F-W angle gamma_bar (radians)
* PHIB d F-W angle phi_bar (radians)
* PSI d F-W angle psi (radians)
* EPS d F-W angle epsilon (radians)
*
* Returned:
* X,Y d CIP unit vector X,Y
*
* Notes:
*
* 1) Naming the following points:
*
* e = J2000.0 ecliptic pole,
* p = GCRS pole
* E = ecliptic pole of date,
* and P = CIP,
*
* the four Fukushima-Williams angles are as follows:
*
* GAMB = gamma = epE
* PHIB = phi = pE
* PSI = psi = pEP
* EPS = epsilon = EP
*
* 2) The matrix representing the combined effects of frame bias,
* precession and nutation is:
*
* NxPxB = R_1(-EPSA).R_3(-PSI).R_1(PHIB).R_3(GAMB)
*
* The returned values x,y are elements (3,1) and (3,2) of the
* matrix. Near J2000.0, they are essentially angles in radians.
*
* Called:
* iau_FW2M F-W angles to r-matrix
* iau_BPN2XY extract CIP X,Y coordinates from NPB matrix
*
* Reference:
*
* Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351
*
* This revision: 2013 September 2
*
* SOFA release 2021-05-12
*
* Copyright (C) 2021 IAU SOFA Board. See notes at end.
*
*-----------------------------------------------------------------------
IMPLICIT NONE
DOUBLE PRECISION GAMB, PHIB, PSI, EPS, X, Y
DOUBLE PRECISION R(3,3)
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Form NxPxB matrix.
CALL iau_FW2M ( GAMB, PHIB, PSI, EPS, R )
* Extract CIP X,Y.
CALL iau_BPN2XY ( R, X, Y )
* Finished.
*+----------------------------------------------------------------------
*
* Copyright (C) 2021
* Standards Of Fundamental Astronomy Board
* of the International Astronomical Union.
*
* =====================
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* =====================
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*-----------------------------------------------------------------------
END