% sets the colormap to grey, using the gray(___) command
% and appends red=[1 0 0] to the end to represent NaN
%
% Example: greynan(200) % produces 200 greylevels, and 1 red level
%
% default is 128 levels (to leave some for other windows)

function simplify_typing_long_commands_like_colormap_gray_128_or_the_like(M)
% returns nothing

if nargin<1
  disp('greynan: setting colormap to default 128 grey levels + red, to make 129 total')
  M = 128;  % default
end%if
if nargin == 1
  if M<256
    disp1=sprintf('greynan: setting colormap to %g grey levels ',M);
    disp2=sprintf('+ red to make %g levels total',M+1);
    disp([disp1 disp2])
  else
    disp('greynan: -----------------------------------------------------------')
    disp1=sprintf('       | %g greylevels + red makes a %g long colormap ',...
		  M,M+1);
    disp2='which is too long';
    disp([disp1 disp2])
    disp('       : -----------------------------------------------------------')
    return
  end%if
end%if

colormap(gray(M))

map = colormap;
map = [map;[1 0 0]];
colormap(map)