# Copyright (C) 1993 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 gramian = dgram (A, B)

#  Usage: gramian = dgram (A, B)
#
#  Returns the discrete controllability and observability gramian.
#
#  dgram (A, B)   returns the discrete controllability gramian.
#  dgram (A', C') returns the observability gramian.

#  Written by R. Bruce Tenison (btenison@eng.auburn.edu)
#  October 1993

  [U, Sig, V] = svd (B);

  gramian = U * dlyap (U'*A*U, Sig*Sig') * U';

endfunction