update packages

[CreaPhase.git] / octave_packages / m / linear-algebra / planerot.m

diff --git a/octave_packages/m/linear-algebra/planerot.m b/octave_packages/m/linear-algebra/planerot.m
new file mode 100644 (file)
index 0000000..56e9109
--- /dev/null
+++ b/octave_packages/m/linear-algebra/planerot.m
@@ -0,0 +1,47 @@
+## Copyright (C) 2008-2012 David Bateman
+##
+## This file is part of Octave.
+##
+## Octave 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.
+##
+## Octave 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 Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[@var{g}, @var{y}] =} planerot (@var{x})
+## Given a two-element column vector, returns the
+## @tex
+## $2 \times 2$ orthogonal matrix
+## @end tex
+## @ifnottex
+## 2 by 2 orthogonal matrix
+## @end ifnottex
+## @var{G} such that
+## @code{@var{y} = @var{g} * @var{x}} and @code{@var{y}(2) = 0}.
+## @seealso{givens}
+## @end deftypefn
+
+function [G, y] = planerot (x)
+  G = givens (x(1), x(2));
+  y = G * x(:);
+endfunction
+
+%!test
+%! x = [3 4];
+%! [g y] = planerot(x);
+%! assert(g - [x(1) x(2); -x(2) x(1)] / sqrt(x(1)^2 + x(2)^2), zeros(2), 2e-8);
+%! assert(y(2), 0, 2e-8);
+
+%!error planerot([0]);
+%!error planerot([0 0 0]);
+%!error planerot();
+