#include "erfa.h"

void eraEcm06(double date1, double date2, double rm[3][3])
/*
**  - - - - - - - - -
**   e r a E c m 0 6
**  - - - - - - - - -
**
**  ICRS equatorial to ecliptic rotation matrix, IAU 2006.
**
**  Given:
**     date1,date2  double         TT as a 2-part Julian date (Note 1)
**
**  Returned:
**     rm           double[3][3]   ICRS to ecliptic rotation matrix
**
**  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.
**
**  1) The matrix is in the sense
**
**        E_ep = rm x P_ICRS,
**
**     where P_ICRS is a vector with respect to ICRS right ascension
**     and declination axes and E_ep is the same vector with respect to
**     the (inertial) ecliptic and equinox of date.
**
**  2) P_ICRS is a free vector, merely a direction, typically of unit
**     magnitude, and not bound to any particular spatial origin, such
**     as the Earth, Sun or SSB.  No assumptions are made about whether
**     it represents starlight and embodies astrometric effects such as
**     parallax or aberration.  The transformation is approximately that
**     between mean J2000.0 right ascension and declination and ecliptic
**     longitude and latitude, with only frame bias (always less than
**     25 mas) to disturb this classical picture.
**
**  Called:
**     eraObl06     mean obliquity, IAU 2006
**     eraPmat06    PB matrix, IAU 2006
**     eraIr        initialize r-matrix to identity
**     eraRx        rotate around X-axis
**     eraRxr       product of two r-matrices
**
**  Copyright (C) 2013-2020, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double ob, bp[3][3], e[3][3];


/* Obliquity, IAU 2006. */
   ob = eraObl06(date1, date2);

/* Precession-bias matrix, IAU 2006. */
   eraPmat06(date1, date2, bp);

/* Equatorial of date to ecliptic matrix. */
   eraIr(e);
   eraRx(ob, e);

/* ICRS to ecliptic coordinates rotation matrix, IAU 2006. */
   eraRxr(e, bp, rm);

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2020, 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,
**  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
**  BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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**  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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**  
*/
