## Copyright (C) 1996, 2000, 2002, 2003, 2004, 2005, 2006, 2007
##               Auburn University.  All rights reserved.
##
## 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 3 of the License, 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, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {} sysupdate (@var{sys}, @var{opt})
## Update the internal representation of a system.
##
## @strong{Inputs}
## @table @var
## @item sys:
## system data structure
## @item opt
## string:
## @table @code
## @item "tf"
## update transfer function form
## @item "zp"
## update zero-pole form
## @item "ss"
## update state space form
## @item "all"
## all of the above
## @end table
## @end table
##
## @strong{Outputs}
## @table @var
## @item retsys
## Contains union of data in sys and requested data.
## If requested data in @var{sys} is already up to date then @var{retsys}=@var{sys}.
## @end table
##
## Conversion to @command{tf} or @command{zp} exits with an error if the system is
## mixed continuous/digital.
## @seealso{tf, ss, zp, sysout, sys2ss, sys2tf, sys2zp}
## @end deftypefn

## Author: John Ingram <ingraje@eng.auburn.edu>
## Created: July 9, 1996

function sys = sysupdate (sys, opt)

  ## check for correct number of inputs
  if (nargin != 2)
    print_usage ();
  elseif (! isstruct (sys))
   error ("first argument must be system data structure");
  elseif (! (strcmp (opt, "tf") || strcmp (opt, "zp")
             || strcmp (opt, "ss") || strcmp (opt, "all")))
    error ("second argument must be \"tf\", \"zp\", \"ss\", or \"all\"");
  endif

  ## check to make sure not trying to make a SISO system out of a MIMO sys
  if ((strcmp (opt, "tf") || strcmp(opt,"zp") || strcmp (opt, "all"))
      && strcmp (sysgettype (sys), "ss") && ! is_siso (sys))
    error ("MIMO -> SISO update requested");
  endif

  ## update transfer function if desired
  if ((strcmp (opt, "tf") || strcmp (opt, "all")) && (! sys.sys(2)))
    ## check to make sure the system is not discrete and continuous
    is_digital (sys);

    ## if original system zero-pole
    if (strcmp (sysgettype (sys), "zp"))
      [sys.num, sys.den] = zp2tf (sys.zer, sys.pol, sys.k);
      sys.sys(2) = 1;
    ## if original system is state-space
    elseif (sys.sys(1) == 2)
      [sys.num, sys.den] = ss2tf (sys.a, sys.b, sys.c, sys.d);
      sys.sys(2) = 1;
    endif
  endif


  ## update zero-pole if desired
  if ((strcmp (opt, "zp") || strcmp (opt, "all")) && ! sys.sys(3))
    ## check to make sure the system is not discrete and continuous
    is_digital (sys);

    ## original system is transfer function
    if (sys.sys(1) == 0)
      [sys.zer, sys.pol, sys.k] = tf2zp (sys.num, sys.den);
      sys.sys(3) = 1;
    ## original system is state-space
    elseif (sys.sys(1) == 2)
      [sys.zer, sys.pol, sys.k] = ss2zp (sys.a, sys.b, sys.c, sys.d);
      sys.sys(3) = 1;
    endif
  endif

  ## update state-space if desired
  if ((strcmp (opt, "ss") || strcmp (opt, "all")) && ! sys.sys(4))
    ## original system is transfer function
    if (sys.sys(1) == 0)
      [sys.a, sys.b, sys.c, sys.d] = tf2ss (sys.num, sys.den);
      sys.sys(4) = 1;
    ## original system is zero-pole
    elseif (sys.sys(1) == 1)
      [sys.a, sys.b, sys.c, sys.d] = zp2ss (sys.zer, sys.pol, sys.k);
      sys.sys(4) = 1;
    endif

    ## create new state names
    sys.stname = __sysdefstname__ (sys.n, sys.nz);
  endif

endfunction