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25
26## -*- texinfo -*-
27## @deftypefn  {} {} feather (@var{u}, @var{v})
28## @deftypefnx {} {} feather (@var{z})
29## @deftypefnx {} {} feather (@dots{}, @var{style})
30## @deftypefnx {} {} feather (@var{hax}, @dots{})
31## @deftypefnx {} {@var{h} =} feather (@dots{})
32##
33## Plot the @code{(@var{u}, @var{v})} components of a vector field emanating
34## from equidistant points on the x-axis.
35##
36## If a single complex argument @var{z} is given, then
37## @code{@var{u} = real (@var{z})} and @code{@var{v} = imag (@var{z})}.
38##
39## The style to use for the plot can be defined with a line style @var{style}
40## of the same format as the @code{plot} command.
41##
42## If the first argument @var{hax} is an axes handle, then plot into this axes,
43## rather than the current axes returned by @code{gca}.
44##
45## The optional return value @var{h} is a vector of graphics handles to the
46## line objects representing the drawn vectors.
47##
48## @example
49## @group
50## phi = [0 : 15 : 360] * pi/180;
51## feather (sin (phi), cos (phi));
52## @end group
53## @end example
54##
55## @seealso{plot, quiver, compass}
56## @end deftypefn
57
58function h = feather (varargin)
59
60  [hax, varargin, nargin] = __plt_get_axis_arg__ ("feather", varargin{:});
61
62  if (nargin == 0 || nargin > 3)
63    print_usage ();
64  endif
65
66  if (nargin == 1 || (nargin == 2 && ! isnumeric (varargin{2})))
67    z = varargin{1}(:).';
68    u = real (z);
69    v = imag (z);
70    have_line_spec = (nargin == 2);
71  elseif (nargin >= 2 && isnumeric (varargin{2}))
72    ioff = 3;
73    u = varargin{1}(:).';
74    v = varargin{2}(:).';
75    have_line_spec = (nargin == 3);
76  else
77    print_usage ();
78  endif
79
80  arrowsize = 0.20;
81  line_spec = "-b";
82
83  if (have_line_spec)
84    arg = varargin{end};
85    if (ischar (arg) || iscellstr (arg))
86      [~, valid] = __pltopt__ ("feather", arg, false);
87      if (valid)
88        line_spec = arg;
89      else
90        error ("feather: invalid linestyle STYLE");
91      endif
92    else
93      error ("feather: invalid linestyle STYLE");
94    endif
95  endif
96
97  ## Matlab draws feather plots, with the arrow head as one continuous line,
98  ## and each arrow separately.  This is completely different from quiver and
99  ## quite ugly.
100  n = length (u);
101  xend = [1 : n] + u;
102  xtmp = [1 : n] + u .* (1 - arrowsize);
103  yend = v;
104  ytmp = v .* (1 - arrowsize);
105  x = [[1 : n]; xend; xtmp - v * arrowsize / 3; xend; ...
106       xtmp + v * arrowsize / 3];
107  y = [zeros(1, n); yend; ytmp + u * arrowsize / 3; yend; ...
108       ytmp - u * arrowsize / 3];
109
110  oldfig = [];
111  if (! isempty (hax))
112    oldfig = get (0, "currentfigure");
113  endif
114  unwind_protect
115    hax = newplot (hax);
116    htmp = plot (x, y, line_spec, [1, n], [0, 0], line_spec);
117  unwind_protect_cleanup
118    if (! isempty (oldfig))
119      set (0, "currentfigure", oldfig);
120    endif
121  end_unwind_protect
122
123  if (nargout > 0)
124    h = htmp;
125  endif
126
127endfunction
128
129
130%!demo
131%! clf;
132%! phi = [0 : 15 : 360] * pi/180;
133%! feather (sin (phi), cos (phi));
134%! axis tight;
135%! title ("feather plot");
136
137## Test input validation
138%!error feather ()
139%!error feather (1,2,3,4)
140%!error feather (1, "-r", 2)
141%!error <invalid linestyle STYLE> feather (1, "abc")
142%!error <invalid linestyle STYLE> feather (1, {1})
143