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+## Copyright (C) 2006, 2007 Michel D. Schmid
+##
+## 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 3 of the License, 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, see
+## <http://www.gnu.org/licenses/>.
+
+## Undocumented internal function
+
+## Author: Michel D. Schmid <michaelschmid@users.sourceforge.net>
+## Adapted-by: jwe
+
+function h = __stem__ (have_z, varargin)
+
+  [ax, varargin, nargin] = __plt_get_axis_arg__ ("stem", varargin{:});
+
+  if (nargin < 1 || nargin > 4)
+    print_usage ();
+  endif
+
+  [x, y, z, dofill, lc, ls, mc, ms] = check_stem_arg (have_z, varargin{:});
+
+  if (dofill)
+    fc = mc;
+  else
+    fc = "none";
+  endif
+
+  newplot ();
+  nx = numel (x);
+  xt = x(:)';
+  xt = [xt; xt; NaN(1, nx)](:);
+  if (have_z)
+    yt = y(:)';
+    yt = [yt; yt; NaN(1, nx)](:);
+    zt = z(:)';
+    zt = [zeros(1, nx); zt; NaN(1, nx)](:);
+  else
+    yt = y(:)';
+    yt = [zeros(1, nx); yt; NaN(1, nx)](:);
+  endif
+
+  oldax = gca ();
+  unwind_protect
+    axes (ax);
+
+    if (have_z)
+      h_stems = plot3 (xt, yt, zt, "color", lc, "linestyle", ls,
+		      x, y, z, "color", mc, "marker", ms, "linestyle", "",
+		      "markerfacecolor", fc);
+
+      h_baseline = [];
+    else
+      h_stems = plot (xt, yt, "color", lc, "linestyle", ls,
+		      x, y, "color", mc, "marker", ms, "linestyle", "",
+		      "markerfacecolor", fc);
+
+      ## Must draw the plot first to get proper x limits.
+      drawnow();
+      x_axis_range = get (gca, "xlim");
+      h_baseline = line (x_axis_range, [0, 0], "color", [0, 0, 0]);
+    endif
+  unwind_protect_cleanup
+    axes (oldax);
+  end_unwind_protect
+
+  h = [h_stems; h_baseline];
+
+endfunction
+
+function [x, y, z, dofill, lc, ls, mc, ms] = check_stem_arg (have_z, varargin)
+
+  ## set specifiers to default values
+  [lc, ls, mc, ms] = set_default_values ();
+  dofill = 0;
+  fill_2 = 0;
+  linespec_2 = 0;
+  z = [];
+
+  ## check input arguments
+  if (nargin == 2)
+    if (have_z)
+      z = varargin{1};
+      x = 1 : rows (z);
+      y = 1 : columns (z);
+    else
+      y = varargin{1};
+      if (isvector (y))
+	x = 1:length(y);
+      elseif (ismatrix (y))
+	x = 1:rows(y);
+      else 
+	error ("stem: Y must be a matrix");
+      endif # in each case, x & y will be defined
+    endif
+  elseif (nargin == 3)
+    ## several possibilities
+    ## 1. the real y data
+    ## 2. 'fill'
+    ## 3. line spec
+    if (ischar (varargin{2}))
+      ## only 2. or 3. possible
+      if (strcmp ("fill", varargin{2}))
+	dofill = 1;
+      else
+	## parse the linespec
+	[lc, ls, mc, ms] = stem_line_spec (varargin{2});
+      endif
+      if (have_z)
+	z = varargin{1};
+	x = 1 : rows (z);
+	y = 1 : columns (z);
+      else
+	y = varargin{1};
+	if (isvector (y))
+	  x = 1:length(y);
+	elseif (ismatrix (y))
+	  x = 1:rows(y);
+	else
+	  error ("stem: Y must be a matrix");
+	endif # in each case, x & y will be defined
+      endif
+    else
+      if (have_z)
+	error ("stem3: must define X, Y and Z");
+      else
+	## must be the real y data
+	x = varargin{1};
+	y = varargin{2};
+	if (! (ismatrix (x) && ismatrix (y)))
+	  error ("stem: X and Y must be matrices");
+	endif
+      endif
+    endif
+  elseif (nargin == 4)
+    ## again several possibilities
+    ## arg2 1. real y
+    ## arg2 2. 'fill' or linespec
+    ## arg3 1. real z
+    ## arg3 2. 'fill' or linespec
+    if (ischar (varargin{2}))
+      ## only arg2 2. / arg3 1. & arg3 3. are possible
+      if (strcmp ("fill", varargin{2}))
+	dofill = 1;
+	fill_2 = 1; # be sure, no second "fill" is in the arguments
+      else
+	## must be a linespec
+	[lc, ls, mc, ms] = stem_line_spec (varargin{2});
+	linespec_2 = 1;
+      endif
+      if (have_z)
+	z = varargin{1};
+	x = 1 : rows (z);
+	y = 1 : columns (z);
+      else
+	y = varargin{1};
+	if (isvector (y))
+	  x = 1:length(y);
+	elseif (ismatrix (y))
+	  x = 1:size(y,1);
+	else
+	  error ("stem: Y must be a matrix");
+	endif # in each case, x & y will be defined
+      endif
+    else
+      if (have_z)
+	x = varargin{1};
+	y = varargin{2};
+	z = varargin{3};
+	if (! (ismatrix (x) && ismatrix (y) && ismatrix (z)))
+	  error ("stem3: X, Y and Z must be matrices");
+	endif
+      else
+	## must be the real y data
+	x = varargin{1};
+	y = varargin{2};
+	if (! (ismatrix (x) && ismatrix (y)))
+	  error ("stem: X and Y must be matrices");
+	endif
+      endif
+    endif # if ischar(varargin{2})
+    if (! have_z)
+      ## varargin{3} must be char...
+      ## check for "fill" ..
+      if (strcmp ("fill", varargin{3}) & fill_2)
+	error ("stem:check_stem_arg: duplicate fill argument");
+      elseif (strcmp("fill", varargin{3}) & linespec_2)
+	## must be "fill"
+	dofill = 1;
+	fill_2 = 1;
+      elseif (strcmp ("fill", varargin{3}) & ! linespec_2)
+	## must be "fill"
+	dofill = 1;
+	fill_2 = 1;
+      elseif (! linespec_2)
+	## must be linespec
+	[lc, ls, mc, ms] = stem_line_spec (varargin{3});
+	linespec_2 = 1;
+      endif
+    endif
+  elseif (nargin == 5)
+    if (have_z)
+      x = varargin{1};
+      y = varargin{2};
+      z = varargin{3};
+      if (! (ismatrix (x) && ismatrix (y) && ismatrix (z)))
+	error ("stem3: X, Y and Z must be matrices");
+      endif
+    else
+      x = varargin{1};
+      y = varargin{2};
+      if (! (ismatrix (x) && ismatrix (y)))
+	error ("X and Y must be matrices");
+      endif
+    endif
+
+    if (! have_z)
+      if (strcmp ("fill", varargin{3}))
+	dofill = 1;
+	fill_2 = 1; # be sure, no second "fill" is in the arguments
+      else
+	## must be a linespec
+	[lc, ls, mc, ms] = stem_line_spec (varargin{3});
+	linespec_2 = 1;
+      endif
+    endif
+
+    ## check for "fill" ..
+    if (strcmp ("fill", varargin{4}) & fill_2)
+      error ("stem:check_stem_arg: duplicate fill argument");
+    elseif (strcmp ("fill", varargin{4}) & linespec_2)
+      ## must be "fill"
+      dofill = 1;
+      fill_2 = 1;
+    elseif (! strcmp ("fill", varargin{4}) & ! linespec_2)
+      ## must be linespec
+      [lc, ls, mc, ms] = stem_line_spec (varargin{4});
+      linespec_2 = 1;
+    endif
+  elseif (nargin == 6 && have_z)
+    x = varargin{1};
+    y = varargin{2};
+    z = varargin{3};
+    if (! (ismatrix (x) && ismatrix (y) && ismatrix (z)))
+      error ("stem3: X, Y and Z must be matrices");
+    endif
+
+    if (strcmp ("fill", varargin{4}))
+      dofill = 1;
+      fill_2 = 1; # be sure, no second "fill" is in the arguments
+    else
+      ## must be a linespec
+      [lc, ls, mc, ms] = stem_line_spec (varargin{4});
+      linespec_2 = 1;
+    endif
+
+    ## check for "fill" ..
+    if (strcmp ("fill", varargin{5}) & fill_2)
+      error ("stem3:check_stem_arg: duplicate fill argument");
+    elseif (strcmp ("fill", varargin{5}) & linespec_2)
+      ## must be "fill"
+      dofill = 1;
+      fill_2 = 1;
+    elseif (! strcmp ("fill", varargin{5}) & ! linespec_2)
+      ## must be linespec
+      [lc, ls, mc, ms] = stem_line_spec (varargin{5});
+      linespec_2 = 1;
+    endif
+  elseif (have_z)
+    error ("stem3: incorrect number of arguments");
+  else
+    error ("stem: incorrect number of arguments");
+  endif
+
+endfunction
+
+function [lc, ls, mc, ms] = stem_line_spec (str)
+  if (! ischar (str))
+    error ("stem:stem_line_spec: wrong argument type, must be \"fill\" or a string of specifiers");
+  endif
+  [lc, ls, mc, ms] = set_default_values ();
+  ## Parse the line specifier string.
+  cur_props = __pltopt__ ("stem", str, false);
+  for i = 1:length(cur_props)
+    if (isfield (cur_props(i), "color") && ! isempty (cur_props(i).color)); # means line color
+      mc = lc = cur_props(i).color;
+    elseif (isfield (cur_props(i), "linestyle"))
+      ls = cur_props(i).linestyle;
+    elseif (isfield (cur_props(i), "marker") && ! strcmp (cur_props(i).marker, "none"))
+      ms = cur_props(i).marker;
+    endif
+  endfor
+endfunction
+
+function [lc, ls, mc, ms] = set_default_values ()
+  ## set default values
+  mc = [1, 0, 0];
+  lc = [1, 0, 0];
+  ls = "-";
+  ms = "o";
+endfunction