## 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} {} zpout (@var{zer}, @var{pol}, @var{k}, @var{x})
## print formatted zero-pole form to the screen.
## @var{x} defaults to the string @code{"s"}
## @end deftypefn
##
## @seealso{polyval, polyvalm, poly, roots, conv, deconv, residue,
## filter, polyderiv, polyinteg, and polyout}

## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
## Created: June 1995

function zpout (zer, pol, k, x)

  save_warn_empty_list_elements = warn_empty_list_elements;
  unwind_protect
    warn_empty_list_elements = 0;

    if (nargin < 3 ) | (nargin > 4) | (nargout != 0 )
      usage("zpout(zer,pol,k[,x])");
    endif

    if( !(isvector(zer) | isempty(zer)) | !(isvector(pol) | isempty(pol)) )
      error("zer, pol must be vectors or empty");
    endif

    if(!isscalar(k))
      error("zpout: argument k must be a scalar.")
    endif

    if (nargin == 3)
      x = "s";
    elseif( ! isstr(x) )
      error("zpout: third argument must be a string");
    endif

    numstring = num2str(k);

    if(length(zer))
      ## find roots at z,s = 0
      nzr = sum(zer == 0);
      if(nzr)
	if(nzr > 1)
	  numstring = [numstring,sprintf(" %s^%d",x,nzr)];
	else
	  numstring = [numstring,sprintf(" %s",x)];
	endif
      endif
      zer = sortcom(-zer);
      for ii=1:length(zer)
	if(zer(ii) != 0)
	  numstring = [numstring,sprintf(" (%s %s)",x,com2str(zer(ii),1) ) ];
	endif
      endfor
    endif

    if(length(pol))
      ## find roots at z,s = 0
      nzr = sum(pol == 0);
      if(nzr)
	if(nzr > 1)
	  denomstring = [sprintf("%s^%d",x,nzr)];
	else
	  denomstring = [sprintf("%s",x)];
	endif
      else
	denomstring = " ";
      endif
      pol = sortcom(-pol);
      for ii=1:length(pol)
	if(pol(ii) != 0)
	  denomstring = [denomstring,sprintf(" (%s %s)",x,com2str(pol(ii),1))];
	endif
      endfor
    endif

    len = max(length(numstring),length(denomstring));
    if(len > 0)
      y = strrep(blanks(len)," ","-");
      disp(numstring)
      if(length(denomstring))
	disp(y)
	disp(denomstring)
      endif
    else
      error ("zpout: empty transfer function")
    end

  unwind_protect_cleanup
    warn_empty_list_elements = save_warn_empty_list_elements;
  end_unwind_protect

endfunction