This is lyap.m in view mode; [Download] [Up]
## Copyright (C) 1996 John W. Eaton
##
## 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 2, 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, write to the Free
## Software Foundation, 59 Temple Place - Suite 330, Boston, MA
## 02111-1307, USA.
## Usage: x = lyap (a, b, c)
## x = lyap (a, c)
##
## If (a, b, c) are specified, then lyap returns the solution of the
## Sylvester equation
##
## a x + x b + c = 0
##
## If only (a, c) are specified, then lyap returns the solution of the
## Lyapunov equation
##
## a x + x a' + c = 0
##
## If b is not square, then lyap returns the solution of either
##
## a' x + x a + b' b = 0
##
## or
##
## a x + x a' + b b' = 0
##
## whichever is appropriate.
##
## Solves by using the Bartels-Stewart algorithm (1972).
## Author: A. S. Hodel <scotte@eng.auburn.edu>
## Created: August 1993
## Adapted-By: jwe
function x = lyap (a, b, c)
if (nargin != 3 && nargin != 2)
usage ("lyap (a, b, c) or lyap (a, c)");
endif
if ((n = is_square(a)) == 0)
error ("lyap: a is not square");
endif
if (nargin == 2)
## Transform Lyapunov equation to Sylvester equation form.
if ((m = is_square (b)) == 0)
if ((m = rows (b)) == n)
## solve a x + x a' + b b' = 0
b = b * b';
c = b;
b = a';
else
## Try to solve a'x + x a + b' b = 0.
m = columns (b);
c = b' * b;
b = a;
a = a';
endif
if (m != n)
error ("lyap: a, b not conformably dimensioned");
endif
else
## If you share your installation of Octave with others, you
## shouldn't remove the following code. Instead, users should
## add
##
## global __disable_lyap_interface_change_warning__;
##
## to their personal ~/.octaverc files. This warning will likely
## disappear for good in some future version of Octave.
if (! exist ("__disable_lyap_interface_change_warning__"))
global __disable_lyap_interface_change_warning__;
warning ("for compatibility with Matlab, lyap now computes");
warning ("");
warning (" A*X + X*A' + C = 0");
warning ("");
warning ("instead of");
warning ("");
warning (" A'*X + X*A + C = 0");
warning ("");
warning ("as in previous versions");
warning ("");
warning ("to completely disable this message, put")
warning ("")
warning (" global __disable_lyap_interface_change_warning__;");
warning ("")
warning ("in your ~/.octaverc file")
endif
c = b;
b = a';
endif
else
## Check dimensions.
if ((m = is_square (b)) == 0)
error ("lyap: b must be square in a sylvester equation");
endif
[n1, m1] = size(c);
if (n != n1 || m != m1)
error("lyap: a, b, c not conformably dimensioned");
endif
endif
## Call octave built-in function.
x = syl (a, b, c);
endfunction
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.