/usr/share/octave/packages/linear-algebra-2.2.0/rotparams.m is in octave-linear-algebra 2.2.0-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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##
## This program is free software; you can redistribute it and/or modify it under
## the terms of the GNU General Public License as published by the Free Software
## Foundation; either version 3 of the License, or (at your option) any later
## version.
##
## This program is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
## details.
##
## You should have received a copy of the GNU General Public License along with
## this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn{Function File} {[@var{vstacked}, @var{astacked}] =} rotparams (@var{rstacked})
## @cindex
## The function w = rotparams (r) - Inverse to rotv().
## Using, @var{w} = rotparams(@var{r}) is such that
## rotv(w)*r' == eye(3).
##
## If used as, [v,a]=rotparams(r) , idem, with v (1 x 3) s.t. w == a*v.
##
## 0 <= norm(w)==a <= pi
##
## :-O !! Does not check if 'r' is a rotation matrix.
##
## Ignores matrices with zero rows or with NaNs. (returns 0 for them)
##
## @seealso{rotv}
## @end deftypefn
function [vstacked, astacked] = rotparams (rstacked)
N = size (rstacked,1) / 3;
## ang = 0 ;
## if length(varargin),
## if strcmp(varargin{1},'ang'), ang = 1; end
## end
ok = all ( ! isnan (rstacked') ) & any ( rstacked' );
ok = min ( reshape (ok,3,N) );
ok = find (ok) ;
## keyboard
vstacked = zeros (N,3);
astacked = zeros (N,1);
for j = ok,
r = rstacked(3*j-2:3*j,:);
[v,f] = eig (r);
f = diag(f);
[m,i] = min (abs (real (f)-1));
v = v(:,i);
w = null (v');
u = w(:,1);
a = u'*r*u;
if a<1,
a = real (acos (u'*r*u));
else
a = 0;
endif
## Check orientation
x=r*u;
if v'*[0 -u(3) u(2); u(3) 0 -u(1);-u(2) u(1) 0]*x < 0, v=-v; endif
if nargout <= 1, v = v*a; endif
vstacked(j,:) = -v';
astacked(j) = a;
endfor
endfunction
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