### 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: 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