## Copyright (C) 1996 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 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 USA.

## -*- texinfo -*-
## @deftypefn {Function File} {[@var{y}, @var{t}] =} step (@var{sys}@{, @var{inp},@var{tstop}, @var{n}@})
## Step response for a linear system.
## The system can be discrete or multivariable (or both).
## If no output arguments are specified, @code{step}
## produces a plot or the step response data for system @var{sys}.
##
## @strong{Inputs}
## @table @var
## @item sys
## System data structure.
## @item inp
## Index of input being excited
## @item tstop
## The argument @var{tstop} (scalar value) denotes the time when the
## simulation should end.
## @item n
## the number of data values.
##
## Both parameters @var{tstop} and @var{n} can be omitted and will be
## computed from the eigenvalues of the A-Matrix.
## @end table
## @strong{Outputs}
## @var{y}, @var{t}: impulse response
##
## When invoked with the output paramter y the plot is not displayed.
## @end deftypefn
## @seealso{impulse and stepimp}

## Author: Kai P. Mueller <mueller@ifr.ing.tu-bs.de>
## Created: September 30, 1997
## based on lsim.m of Scottedward Hodel

function [y, t] = step (sys, inp, tstop, n)

  if((nargin < 1) || (nargin > 4))
    usage("[y, u] = step(sys[, inp, tstop, n])");
  endif

  if(nargout > 2)
    usage("[y, u] = step(sys[, inp, tstop, n])");
  endif

  if(!is_struct(sys))
    error("step: sys must be a system data structure.");
  endif

  if (nargout == 0)
    switch (nargin)
      case (1)
        stepimp(1, sys);
      case (2)
        stepimp(1, sys, inp);
      case (3)
        stepimp(1, sys, inp, tstop);
      case (4)
        stepimp(1, sys, inp, tstop, n);
    endswitch
  else
    switch (nargin)
      case (1)
        [y, t] = stepimp(1, sys);
      case (2)
        [y, t] = stepimp(1, sys, inp);
      case (3)
        [y, t] = stepimp(1, sys, inp, tstop);
      case (4)
        [y, t] = stepimp(1, sys, inp, tstop, n);
    endswitch
  endif

endfunction