## Copyright (C) 1996, 1997 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: 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.

## Author: R. Bruce Tenison <btenison@eng.auburn.edu>
## Created: October 1993
## Adapted-By: jwe


function gramian = dgram (A, B)

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

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

endfunction