new file mode 100644
--- /dev/null
+++ b/scripts/control/dcgain.m
@@ -0,0 +1,57 @@
+# 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)
+#
+# See also: (nothing)
+
+# Written by Kai P Mueller (mueller@ifr.ing.tu-bs.de) October 1, 1997
+# Updated
+# $Revision: 1.1.1.1 $
+# $Log: dcgain.m,v $
+# Revision 1.1.1.1  1998/05/19 20:24:06  jwe
+#
+# Revision 1.3  1997/12/01 16:51:50  scotte
+# updated by Mueller 27 Nov 97
+#
+# Revision 1.1  1997/11/11  17:32:46  mueller
+# Initial revision
+#
+
+  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 = sys.a;
+  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 = -sys.c / aa * sys.b + sys.d;
+  endif
+endfunction