## 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, 59 Temple Place, Suite 330, Boston, MA 02111 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{Inputs}
##  @var{sys} system data structure
## 
## @strong{Outputs}
## if omitted, the poles and zeros are plotted on the screen.
##           otherwise, pol, zer are returned as the system poles and zeros.
##           (see sys2zp for a preferable function call)
## @end deftypefn
 
function [zer, pol]=pzmap (sys)

  save_emp = empty_list_elements_ok;

  empty_list_elements_ok = 1;

  if(nargin != 1)
    usage("pzmap(sys) or [zer,pol] = pzmap(sys)"); 
  elseif (!is_struct(sys));
    error("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
  gset nologscale xy;
  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(["Re(",varstr,")"]);
  ylabel(["Im(",varstr,")"]);
  grid;

  ## compute axis limits
  axis(axis2dlim([zerdata;poldata]));
  grid
  ## finally, 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
  replot

  empty_list_elements_ok = save_emp;

endfunction