## 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}] =} impulse (@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{impulse}
##  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
 
## See also:  impulse, stepimp

## step: Step response for a linear system.
##       The system can be discrete or multivariable (or both).
##
## [y, t] = step(sys[, inp, tstop, n])
## Produces a plot or the step response data for system sys.
##
## The argument tstop (scalar value) denotes the time when the
## simulation should end. The Parameter n is the number of data values.
## Both parameters tstop and n can be ommitted and will be
## computed from the eigenvalues of the A-Matrix.
##
## When the step function is invoked with the output parameter y
## a plot is not displayed.
##
## See also: impulse, stepimp

function [y, t] = step (sys, inp, tstop, n)
## Written by Kai P. Mueller September 30, 1997
## based on lsim.m of Scottedward Hodel
## modified by

  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