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#include "erfa.h"
void eraRm2v(double r[3][3], double w[3])
/*
** - - - - - - - -
** e r a R m 2 v
** - - - - - - - -
**
** Express an r-matrix as an r-vector.
**
** Given:
** r double[3][3] rotation matrix
**
** Returned:
** w double[3] rotation vector (Note 1)
**
** Notes:
**
** 1) A rotation matrix describes a rotation through some angle about
** some arbitrary axis called the Euler axis. The "rotation vector"
** returned by this function has the same direction as the Euler axis,
** and its magnitude is the angle in radians. (The magnitude and
** direction can be separated by means of the function eraPn.)
**
** 2) If r is null, so is the result. If r is not a rotation matrix
** the result is undefined; r must be proper (i.e. have a positive
** determinant) and real orthogonal (inverse = transpose).
**
** 3) The reference frame rotates clockwise as seen looking along
** the rotation vector from the origin.
**
** Copyright (C) 2013-2016, NumFOCUS Foundation.
** Derived, with permission, from the SOFA library. See notes at end of file.
*/
{
double x, y, z, s2, c2, phi, f;
x = r[1][2] - r[2][1];
y = r[2][0] - r[0][2];
z = r[0][1] - r[1][0];
s2 = sqrt(x*x + y*y + z*z);
if (s2 > 0) {
c2 = r[0][0] + r[1][1] + r[2][2] - 1.0;
phi = atan2(s2, c2);
f = phi / s2;
w[0] = x * f;
w[1] = y * f;
w[2] = z * f;
} else {
w[0] = 0.0;
w[1] = 0.0;
w[2] = 0.0;
}
return;
}
/*----------------------------------------------------------------------
**
**
** Copyright (C) 2013-2016, 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;
** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
** POSSIBILITY OF SUCH DAMAGE.
**
*/
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