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25
26## -*- texinfo -*-
27## @deftypefn  {} {@var{map} =} prism ()
28## @deftypefnx {} {@var{map} =} prism (@var{n})
29## Create color colormap.  This colormap cycles through red, orange, yellow,
30## green, blue and violet with each index change.
31##
32## The argument @var{n} must be a scalar.
33## If unspecified, the length of the current colormap, or 64, is used.
34## @seealso{colormap}
35## @end deftypefn
36
37function map = prism (n)
38
39  if (nargin > 1)
40    print_usage ();
41  elseif (nargin == 1)
42    if (! isscalar (n))
43      error ("prism: N must be a scalar");
44    endif
45    n = double (n);
46  else
47    hf = get (0, "currentfigure");
48    if (! isempty (hf))
49      n = rows (get (hf, "colormap"));
50    else
51      n = 64;
52    endif
53  endif
54  if (n == 1)
55    map = [1 0 0];
56  elseif (n > 1)
57    C = [1, 0, 0; 1, 1/2, 0; 1, 1, 0; 0, 1, 0; 0, 0, 1; 2/3, 0, 1];
58    map = C(rem (0:(n-1), 6) + 1, :);
59  else
60    map = zeros (0, 3);
61  endif
62
63endfunction
64
65
66%!demo
67%! ## Show the 'prism' colormap profile and as an image
68%! cmap = prism (18); # 6 colors, therefore cycle 3 times
69%! subplot (2, 1, 1);
70%!  rgbplot (cmap, "composite");
71%! subplot (2, 1, 2);
72%!  rgbplot (cmap);
73