#include "erfa.h"

void eraFw2xy(double gamb, double phib, double psi, double eps,
              double *x, double *y)
/*
**  - - - - - - - - -
**   e r a F w 2 x y
**  - - - - - - - - -
**
**  CIP X,Y given Fukushima-Williams bias-precession-nutation angles.
**
**  Given:
**     gamb     double    F-W angle gamma_bar (radians)
**     phib     double    F-W angle phi_bar (radians)
**     psi      double    F-W angle psi (radians)
**     eps      double    F-W angle epsilon (radians)
**
**  Returned:
**     x,y      double    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 [2][0] and [2][1] of the
**     matrix.  Near J2000.0, they are essentially angles in radians.
**
**  Called:
**     eraFw2m      F-W angles to r-matrix
**     eraBpn2xy    extract CIP X,Y coordinates from NPB matrix
**
**  Reference:
**
**     Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351
**
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double r[3][3];

/* Form NxPxB matrix. */
   eraFw2m(gamb, phib, psi, eps, r);

/* Extract CIP X,Y. */
   eraBpn2xy(r, x, y);

   return;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  All rights reserved.
**  
**  This library is derived, with permission, from the International
**  Astronomical Union's "Standards of Fundamental Astronomy" library,
**  available from http://www.iausofa.org.
**  
**  The ERFA version is intended to retain identical functionality to
**  the SOFA library, but made distinct through different function and
**  file names, as set out in the SOFA license conditions.  The SOFA
**  original has a role as a reference standard for the IAU and IERS,
**  and consequently redistribution is permitted only in its unaltered
**  state.  The ERFA version is not subject to this restriction and
**  therefore can be included in distributions which do not support the
**  concept of "read only" software.
**  
**  Although the intent is to replicate the SOFA API (other than
**  replacement of prefix names) and results (with the exception of
**  bugs;  any that are discovered will be fixed), SOFA is not
**  responsible for any errors found in this version of the library.
**  
**  If you wish to acknowledge the SOFA heritage, please acknowledge
**  that you are using a library derived from SOFA, rather than SOFA
**  itself.
**  
**  
**  TERMS AND CONDITIONS
**  
**  Redistribution and use in source and binary forms, with or without
**  modification, are permitted provided that the following conditions
**  are met:
**  
**  1 Redistributions of source code must retain the above copyright
**    notice, this list of conditions and the following disclaimer.
**  
**  2 Redistributions in binary form must reproduce the above copyright
**    notice, this list of conditions and the following disclaimer in
**    the documentation and/or other materials provided with the
**    distribution.
**  
**  3 Neither the name of the Standards Of Fundamental Astronomy Board,
**    the International Astronomical Union nor the names of its
**    contributors may be used to endorse or promote products derived
**    from this software without specific prior written permission.
**  
**  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
**  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
**  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
**  FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
**  COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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**  
*/