## Copyright (C) 1996, 1998 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, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301 USA.

## -*- texinfo -*-
## @deftypefn {Function File} {[@var{zer}, @var{pol}] =} pzmap (@var{sys})
## Plots the zeros and poles of a system in the complex plane.
##
## @strong{Input}
## @table @var
## @item sys
## System data structure.
## @end table
##
## @strong{Outputs}
## @table @var
## @item pol
## @item zer
## if omitted, the poles and zeros are plotted on the screen.
## otherwise, @var{pol} and @var{zer} are returned as the 
## system poles and zeros (see @command{sys2zp} for a preferable function call).
## @end table
## @end deftypefn

function [zer, pol] = pzmap (sys)

  if (nargin != 1)
    print_usage ();
  elseif (! isstruct (sys));
    error ("pzmap: sys must be in system format");
  endif

  [zer, pol] = sys2zp (sys);

  ## force to column vectors, split into real, imaginary parts
  zerdata = poldata = [];
  if (length (zer))
    zer = reshape (zer, length (zer), 1);
    zerdata = [real(zer(:,1)), imag(zer(:,1))];
  endif
  if (length (pol))
    pol = reshape (pol, length (pol), 1);
    poldata = [real(pol(:,1)), imag(pol(:,1))];
  endif

  ## determine continuous or discrete plane
  vars = "sz";
  varstr = vars(is_digital (sys) + 1);

  ## Plot the data

  if (length (zer) == 0)
    plot (poldata(:,1), poldata(:,2), "@12 ;poles (no zeros);");
  elseif (length (pol) == 0)
    plot (zerdata(:,1), zerdata(:,2), "@31 ;zeros (no poles);");
  else
    plot (zerdata(:,1), zerdata(:,2), "@31 ;zeros;",
	  poldata(:,1), poldata(:,2), "@12 ;poles;");
  endif

  if (is_siso (sys))
    title (sprintf ("Pole-zero map from %s to %s",
		    sysgetsignals (sys, "in", 1, 1),
		    sysgetsignals (sys, "out", 1, 1)));
  endif

  xlabel (sprintf ("Re(%s)", varstr));
  ylabel (sprintf ("Im(%s)", varstr));
  grid ("on");

  ## compute axis limits
  axis (axis2dlim ([zerdata; poldata]));

endfunction