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dcgain.m
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1999-03-05
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# Copyright (C) 1993, 1994, 1995 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, 675 Mass Ave, Cambridge, MA 02139, USA.
function gm = dcgain(sys, tol)
# Usage: gm = dcgain(sys[, tol])
# Returns dc-gain matrix. If dc-gain is infinity
# an empty matrix is returned.
# The argument tol is an optional tolerance for the condition
# number of A-Matrix in sys (default tol = 1.0e-10)
# Prints a warning message of the system is unstable.
#
# Written by Kai P Mueller (mueller@ifr.ing.tu-bs.de) October 1, 1997
if((nargin < 1) || (nargin > 2) || (nargout > 1))
usage("[gm, ok] = dcgain(sys[, tol])");
endif
if(!is_struct(sys))
error("dcgain: first argument is not a system data structure.")
endif
sys = sysupdate(sys, "ss");
[aa,bb,cc,dd] = sys2ss(sys);
if (is_digital(sys)) aa = aa - eye(size(aa)); endif
if (nargin == 1) tol = 1.0e-10; endif
r = rank(aa, tol);
if (r < rows(aa))
gm = [];
else
gm = -cc / aa * bb + dd;
endif
if(!is_stable(sys))
[nn,nz,mm,pp] = sysdimensions(sys);
warning("dcgain: unstable system; dimensions [nc=%d,nz=%d,mm=%d,pp=%d]", ...
nn,nz,mm,pp);
endif
endfunction