### 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: [n, m, p] = abcddim (a, b, c, d)
##
## Check for compatibility of the dimensions of the matrices defining
## the linear system (a, b, c, d).
##
## Returns n = number of system states,
##         m = number of system inputs,
##         p = number of system outputs.
##
## Returns n = m = p = -1 if the system is not compatible.

function [n, m, p] = abcddim (a, b, c, d)

  ## Written by A. S. Hodel (scotte@eng.auburn.edu) August 1993.

  if (nargin != 4)
    error ("usage: abcddim (a, b, c, d)");
  endif

  n = m = p = -1;

  [an, am] = size(a);
  if (an != am)
    error ("abcddim: a is not square");
  endif

  [bn, bm] = size(b);
  if (bn != am)
    error ("abcddim: a and b are not compatible");
  endif

  [cn, cm] = size(c);
  if (cm != an)
    error ("abcddim: a and c are not compatible");
  endif

  [dn, dm] = size(d);
  if (cn != dn)
    error ("abcddim: c and d are not compatible");
  endif

  if (bm != dm)
    error ("abcddim: b and d are not compatible");
  endif

  n = an;
  m = bm;
  p = cn;

endfunction