## Copyright (C) 1997, 2000, 2004, 2005, 2006, 2007 Kai P. Mueller
##
##
## This program 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 3 of the License, or (at
## your option) any later version.
##
## This program 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 this program; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {@var{retval} =} is_abcd (@var{a}, @var{b}, @var{c}, @var{d})
##  Returns @var{retval} = 1 if the dimensions of @var{a}, @var{b},
##  @var{c}, @var{d} are compatible, otherwise @var{retval} = 0 with an
##  appropriate diagnostic message printed to the screen.  The matrices
##  @var{b}, @var{c}, or @var{d} may be omitted.
## @seealso{abcddim}
## @end deftypefn

## Author: Kai P. Mueller <mueller@ifr.ing.tu-bs.de>
## Created: November 4, 1997
## based on is_controllable.m of Scottedward Hodel

function retval = is_abcd (a, b, c, d)

  retval = 0;

  switch (nargin)
    case 1
      ## A only
      [na, ma] = size (a);
      if (na != ma)
        disp ("Matrix A ist not square.")
      endif
    case 2
      ## A, B only
      [na, ma] = size (a);
      [nb, mb] = size(b);
      if (na != ma)
        disp ("Matrix A ist not square.")
        return;
      endif
      if (na != nb)
        disp ("A and B column dimension different.")
        return;
      endif
    case 3
      ## A, B, C only
      [na, ma] = size(a);
      [nb, mb] = size(b);
      [nc, mc] = size(c);
      if (na != ma)
        disp ("Matrix A ist not square.")
        return;
      endif
      if (na != nb)
        disp ("A and B column dimensions not compatible.")
        return;
      endif
      if (ma != mc)
        disp ("A and C row dimensions not compatible.")
        return;
      endif
    case 4
      ## all matrices A, B, C, D
      [na, ma] = size(a);
      [nb, mb] = size(b);
      [nc, mc] = size(c);
      [nd, md] = size(d);
      if (na != ma)
        disp ("Matrix A ist not square.")
        return;
      endif
      if (na != nb)
        disp ("A and B column dimensions not compatible.")
        return;
      endif
      if (ma != mc)
        disp ("A and C row dimensions not compatible.")
        return;
      endif
      if (mb != md)
        disp ("B and D row dimensions not compatible.")
        return;
      endif
      if (nc != nd)
        disp ("C and D column dimensions not compatible.")
        return;
      endif
    otherwise
      print_usage ();
  endswitch
  ## all tests passed, signal ok.
  retval = 1;

endfunction
