## Copyright (C) 1998, 2000, 2002, 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} {[@var{stname}, @var{inname}, @var{outname}, @var{yd}] =} sysgetsignals (@var{sys})
## @deftypefnx {Function File} {@var{siglist} =} sysgetsignals (@var{sys}, @var{sigid})
## @deftypefnx {Function File} {@var{signame} =} sysgetsignals (@var{sys}, @var{sigid}, @var{signum}, @var{strflg})
## Get signal names from a system
##
## @strong{Inputs}
## @table @var
## @item sys
## system data structure for the state space system
##
## @item sigid
## signal id.  String.  Must be one of
## @table @code
## @item "in"
## input signals
## @item "out"
## output signals
## @item "st"
## stage signals
## @item "yd"
## value of logical vector @var{yd}
## @end table
##
## @item signum
## index(indices) or name(s) or signals; see @code{sysidx}
##
## @item strflg
## flag to return a string instead of a cell array;  Values:
## @table @code
## @item 0
## (default) return a cell array (even if signum specifies an individual signal)
##
## @item 1
## return a string.  Exits with an error if signum does not specify an 
## individual signal.
## @end table
##
## @end table
##
## @strong{Outputs}
## @table @bullet
## @item If @var{sigid} is not specified:
## @table @var
## @item stname
## @itemx inname
## @itemx outname
## signal names (cell array of strings);  names of states,
## inputs, and outputs, respectively.
## @item yd
## binary vector; @var{yd}(@var{ii}) is nonzero if output @var{ii} is
## discrete.
## @end table
##
## @item If @var{sigid} is specified but @var{signum} is not specified:
## @table @code
## @item sigid="in"
## @var{siglist} is set to the cell array of input names.
##
## @item sigid="out"
## @var{siglist} is set to the cell array of output names.
##
## @item sigid="st"
## @var{siglist} is set to the cell array of state names.
##
## stage signals
## @item sigid="yd"
## @var{siglist} is set to logical vector indicating discrete outputs;
## @var{siglist}(@var{ii}) = 0 indicates that output @var{ii} is continuous
## (unsampled), otherwise it is discrete.
##
## @end table
##
## @item If the first three input arguments are specified:
## @var{signame} is a cell array of the specified signal names (@var{sigid} is 
## @code{"in"}, @code{"out"}, or @code{"st"}), or else the logical flag
## indicating whether output(s) @var{signum} is(are) discrete (@var{sigval}=1)
## or continuous (@var{sigval}=0).
## @end table
##
## @strong{Examples} (From @code{sysrepdemo})
## @example
## octave> sys=ss(rand(4),rand(4,2),rand(3,4));
## octave># get all signal names
## octave> [Ast,Ain,Aout,Ayd] = sysgetsignals(sys)
## Ast =
## (
##   [1] = x_1
##   [2] = x_2
##   [3] = x_3
##   [4] = x_4
## )
## Ain =
## (
##   [1] = u_1
##   [2] = u_2
## )
## Aout =
## (
##   [1] = y_1
##   [2] = y_2
##   [3] = y_3
## )
## Ayd =
##
##   0  0  0
## octave> # get only input signal names:
## octave> Ain = sysgetsignals(sys,"in")
## Ain =
## (
##   [1] = u_1
##   [2] = u_2
## )
## octave> # get name of output 2 (in cell array):
## octave> Aout = sysgetsignals(sys,"out",2)
## Aout =
## (
##   [1] = y_2
## )
## octave> # get name of output 2 (as string):
## octave> Aout = sysgetsignals(sys,"out",2,1)
## Aout = y_2
## @end example
## @end deftypefn

function [stname, inname, outname, yd] = sysgetsignals (sys, sigid, signum, strflg)

  ## Adapted from ss

  if (nargin < 1 || nargin > 4)
    print_usage ();
  elseif (! isstruct (sys))
    error ("input argument must be a system data structure");
  endif
  if (nargin < 4)
    strflg = 0;
  endif

  if (nargin == 1)
    sys = sysupdate (sys, "ss");          #make sure ss is up to date
    stname = sysgetsignals (sys, "st");
    inname = sysgetsignals (sys, "in");
    outname = sysgetsignals (sys, "out");
    yd = sysgetsignals (sys, "yd");
  elseif (! (ischar (sigid) && min (size (sigid)) == 1))
    error ("sigid(%dx%d) must be a string)", rows (sigid), columns (sigid));
  else
    if (strcmp ("st", sigid))
      stname = sys.stname;
    elseif (strcmp ("in", sigid))
      stname = sys.inname;
    elseif (strcmp ("out", sigid))
      stname = sys.outname;
    elseif (strcmp ("yd", sigid))
      stname = vec(sys.yd)';
    else
      error ("sigid=%s must be \"st\", \"in\", \"out\", or \"yd\"", sigid);
    endif
    if (nargin >= 3)
      if (is_signal_list (signum) || ischar (signum))
        signum = cellidx (stname, signum);
      endif
      if (max (signum) > length (stname))
        error ("sysgetsignals(sys,\"%s\",%d):only %d entries",
               sigid, signum, rows (stname));
      else
        if (! isscalar (strflg))
          error ("strflg must be a scalar");
        endif
        switch (strflg)
        case 0
          stname = stname (signum);
        case 1
          if (length (signum) > 1)
            error ("strflg=1, length(signum) = %d", length (signum));
          endif
          stname = stname{signum};
        otherwise
          error ("invalid value of strflg = %e", strflg);
        endswitch
      endif
    endif
  endif

endfunction