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## -*- texinfo -*-
## @deftypefn  {} {@var{map} =} hot ()
## @deftypefnx {} {@var{map} =} hot (@var{n})
## Create color colormap.  This colormap ranges from black through dark red,
## red, orange, yellow, to white.
##
## The argument @var{n} must be a scalar.
## If @var{n} is not specified the length of the current colormap is used.  If
## there is no current colormap the default value of 256 is used.
## @seealso{colormap}
## @end deftypefn

function map = hot (n)

  if (nargin == 1)
    if (! (isscalar (n) && isreal (n) && n == fix (n)))
      error ("hot: N must be a scalar integer");
    endif
    n = double (n);
  else
    hf = get (0, "currentfigure");
    if (! isempty (hf))
      n = rows (get (hf, "colormap"));
    else
      n = 256;
    endif
  endif
  if (n == 1)
    map = [1, 1, 1];
  elseif (n == 2)
    map = [1, 1, 1/2
           1, 1,  1 ];
  elseif (n > 2)
    idx = floor (3/8 * n);
    nel = idx;

    r = ones (n, 1);
    r(1:idx, 1) = [1:nel]' / nel;

    g = zeros (n, 1);
    g(idx+1:2*idx, 1) = r(1:idx);
    g(2*idx+1:end, 1) = 1;

    idx = 2*idx + 1;   # approximately 3/4 *n
    nel = n - idx + 1;

    b = zeros (n, 1);
    b(idx:end, 1) = [1:nel]' / nel;

    map = [r, g, b];
  else
    map = zeros (0, 3);
  endif

endfunction


%!demo
%! ## Show the 'hot' colormap profile and as an image
%! cmap = hot (256);
%! subplot (2, 1, 1);
%!  rgbplot (cmap, "composite");
%! subplot (2, 1, 2);
%!  rgbplot (cmap);

%!assert (size (hot ()), [256, 3])
%!assert (size (hot (16)), [16, 3])

%!assert (hot (1), [1, 1, 1])
%!assert (hot (true), double ([1, 1, 1]))
%!assert (hot (char (1)), double ([1, 1, 1]))
%!assert (hot (int32 (1)), double ([1, 1, 1]))
%!assert (hot (2), [1, 1, 1/2; 1, 1, 1])
%!assert (hot (3), [1, 0, 0; 1, 1, 0; 1 1 1])

%!assert (hot (0), zeros (0, 3))
%!assert (hot (-1), zeros (0, 3))

%!test
%! a = [0.25, 0,    0;
%!      0.50, 0,    0;
%!      0.75, 0,    0;
%!      1,    0,    0;
%!      1,    0.25, 0;
%!      1,    0.50, 0;
%!      1,    0.75, 0;
%!      1,    1,    0;
%!      1,    1,    1/3;
%!      1,    1,    2/3;
%!      1,    1,    1];
%! assert (hot (11), a, eps);

## Input validation
%!error <N must be a scalar integer> hot ("foo")
%!error <N must be a scalar integer> hot ([1, 2, 3])
%!error <N must be a scalar integer> hot ({1, 2, 3})