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########################################################################
##
## Copyright (C) 1999-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## 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
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{map} =} jet ()
## @deftypefnx {} {@var{map} =} jet (@var{n})
## Create color colormap. This colormap ranges from dark blue through blue,
## cyan, green, yellow, red, to dark red.
##
## The argument @var{n} must be a scalar.
## If unspecified, the length of the current colormap, or 64, is used.
##
## Programming Note: The @code{jet} colormap is not perceptually uniform.
## Try the @code{viridis} colormap if that is important. For a drop-in
## replacement for @code{jet} with better perceptual characteristics try
## the @code{turbo} colormap.
## @seealso{colormap, turbo}
## @end deftypefn
function map = jet (n)
if (nargin == 1)
if (! isscalar (n))
error ("jet: N must be a scalar");
endif
n = double (n);
else
hf = get (0, "currentfigure");
if (! isempty (hf))
n = rows (get (hf, "colormap"));
else
n = 64;
endif
endif
if (n == 1)
map = [0, 1, 1];
elseif (n == 2)
map = [0, 0, 1
0, 1, 1];
elseif (n > 2)
nel = ceil (n/4); # number of elements
idx1 = ceil (3/8 * n) + 1; # ~3/8*n for large n
if (mod (n, 8) == 2)
idx1 += 1;
endif
idx2 = idx1 + nel - 1; # ~5/8*n for large n
idx3 = min (idx2 + nel, n); # ~7/8*n for large n
r = zeros (n, 1);
r(idx1:idx2, 1) = [1:nel] / nel;
r(idx2:idx3, 1) = 1;
nel2 = n - idx3;
r(idx3:(idx3+nel2), 1) = [nel:-1:(nel - nel2)] / nel;
idx1 = idx1 - nel; # ~1/8*n for large n
idx2 = idx1 + nel - 1; # ~3/8*n for large n
idx3 = min (idx2 + nel, n); # ~5/8*n for large n
g = zeros (n, 1);
g(idx1:idx2, 1) = [1:nel] / nel;
g(idx2:idx3, 1) = 1;
nel2 = min (nel, n - idx3);
g(idx3:(idx3+nel2), 1) = [nel:-1:(nel - nel2)] / nel;
idx1 = max (idx2 - nel, 1); # ~1/8*n for large n
idx2 = idx2; # ~3/8*n for large n
idx3 = idx3; # ~5/8*n for large n
b = zeros (n, 1);
nel2 = min (nel, idx1-1);
b(1:idx1, 1) = [(nel - nel2):nel] / nel;
b(idx1:idx2, 1) = 1;
nel2 = min (nel, n - idx3);
b(idx2:(idx2+nel2), 1) = [nel:-1:(nel - nel2)] / nel;
map = [r, g, b];
else
map = zeros (0, 3);
endif
endfunction
%!demo
%! ## Show the 'jet' colormap profile and as an image
%! cmap = jet (256);
%! subplot (2, 1, 1);
%! rgbplot (cmap, "composite");
%! subplot (2, 1, 2);
%! rgbplot (cmap);
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