Merry Christmas!

Stefan Güttel & Nick Hale, 13th December 2011

Chebfun has long been a popular medium for sending birthday wishes [1], and we now take this opportunity to wish you a Merry Christmas and Happy Holidays!

function XmasCard

"Kling Gloeckchen Klingelingeling..."

v1 = [ '777744557979777-5555227744444---' ...
       '2-2244004444222-5-5577225555444-' ...
       '2-224-6-7777222-449977669999777-' ];
v2 = [ '444400224545444-22222-2-00000---' ...
       '7-7-7-7-7754222-2-2-4-5-2245000-' ...
       '6-667-9-7777777-2-2-2-246666000-' ];
v3 = [ '44444444444444442222222200000---' ...
       '77777777777755552222222222220000' ...
       '2222000044447777666666666666777-' ];
% Convert to a tune (a chebfun quasimatrix) with STR2TUNE
c1 = str2tune([ v1 , v1(1:32) ]);       % Repeat
c2 = str2tune([ v2 , v2(1:32) ]) - 12;  % Subtract an octave and repeat
c3 = str2tune([ v3 , v3(1:32) ]) - 24;  % Subtract two octaves and repeat
% Play with some chorus added to c1
c = [ c1-.09 , c1+0.09 , c2 , c3 ];
% Send the quasimatrix to CHEBTUNE
[Y Fs] = chebtune(c,20);

% Graphics
plot(.6*scribble('Merry Xmas!'),'r','linewidth',2);
axis([-1,1,-1,1]); axis off; set(gcf,'Color',[1,1,1]), hold on
nr = 40;
s = 2*rand(nr,1)+2i*rand(nr,1)-1-1i;
p = plot(s,'b*');
for j = 1:1000,
    s = s + 0.001*randn(nr,1) - 0.005i*rand(nr,1);
    ind = find(abs(real(s))>1 | abs(imag(s))>1);
    s(ind) = 2*rand(length(ind),1)-1+1i;
    set(p,'XData',real(s),'YData',imag(s));
    drawnow; pause(0.01);
    M(j) = getframe;
end

% Write to file: (Uncomment the below if you wish to store the output of
% this file to .wav and .gif files).

% wavwrite(Y,Fs,8,'html/XmasCard.wav')
% for j = 1:3:min(300,numel(M))
% im = frame2im(M(j));
% [imind,cm] = rgb2ind(im,16);
%     if j == 1;
%         imwrite(imind,cm,'XmasCard.gif','gif', ...
%             'Loopcount',inf,'DelayTime',1e-5);
%     else
%         imwrite(imind,cm,'XmasCard.gif','gif', ...
%             'WriteMode','append','DelayTime',1e-5);
%     end
% end

end

function c = str2tune(str)
    %STR2TUNE   Converts string of notes to a Chebfun
    %   which can be played as a melody by CHEBTUNE.
    %
    %   Example 1:
    %      c = str2tune('0245--5420');
    %      chebtune(c);
    %
    %   Example 2:
    %      c = str2tune('0123456789abcdef');
    %      chebtune(c);
    %
    %   See also chebtune.

    c = chebfun('NaN',[0,1]);
    lgth = length(str);
    left  = 0;
    t_old = myhex2dec(str(1));

    for j = 2:lgth,
        right = (j-1)/lgth;
        t = myhex2dec(str(j));
        if t == t_old,
            continue;
        end;
        if ~isempty(t_old),
            c(domain([left,right])) = t_old;
        end;
        t_old = t;
        left = right;
    end

    if ~isempty(t_old),
        c(domain([left,1])) = t_old;
    end

    function s = myhex2dec(s)
        if ~strcmp(s,'-')
            s = hex2dec(s);
        else
            s = [];
        end
    end
end

References

[1] http://www.maths.ox.ac.uk/chebfun/examples/fun/html/Birthday.shtml

[2] http://www.maths.ox.ac.uk/chebfun/examples/fun/html/AudibleChebfuns.shtml