## Copyright (C) 1999,2000  Kai Habel
##
## This program 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 2 of the License, or
## (at your option) any later version.
##
## This program 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 this program; if not, write to the Free Software
## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

## -*- texinfo -*-
## @deftypefn {Function File} {} prism (@var{n})
## Create color colormap. 
## (cycling trough red, orange, yellow, green, blue and violet)
## The argument @var{n} should be a scalar.  If it
## is omitted, the length of the current colormap or 64 is assumed.
## @end deftypefn
## @seealso{colormap}

## Author:  Kai Habel <kai.habel@gmx.de>

function map = prism (number)
  global __current_color_map__

  if (nargin == 0)
    if exist("__current_color_map__")
      number = rows (__current_color_map__);
    else
      number = 64;
    endif
  elseif (nargin == 1)
    if (! is_scalar (number))
      error ("prism: argument must be a scalar");
    endif
  else
    usage ("prism (number)");
  endif

  p = [1, 0, 0; 1, 1/2, 0; 1, 1, 0; 0, 1, 0; 0, 0, 1; 2/3, 0, 1];

  if (rem (number, 6) == 0)
    map = kron(ones (fix (number / 6), 1), p);
  else
    map = [kron(ones (fix (number / 6), 1), p); p(1:rem (number, 6), :)];
  endif

endfunction