Matlab Simulation: Point (symbol) Moving from start point to end point and back

Question

I would like to create an animation to demonstrate LDPC coding which is based on Sum-Product Algorithm

So far I have created a graph which shows the connections betw

Answer 1

I believe the best way to learn is by example. So I suggest you look at the demo lorenz which comes with MATLAB:

edit lorenz

For other cool animations, look for orbits.m and swinger.m demos part of Cleve Moler's book: Experiments with MATLAB

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I show here a simple animation of a point moving along a circular path. The hold idea boils down to using EraseMode set to xor, and updating XData and YData of the point for each iteration:

%# coordinates
t = (0:.01:2*pi)';         %# 'fix SO syntax highlight
D = [cos(t) -sin(t)];

%# setup a figure and axis
hFig = figure('Backingstore','off', 'DoubleBuffer','on');
hAx = axes('Parent',hFig, 'XLim',[-1 1], 'YLim',[-1 1], ...
          'Drawmode','fast', 'NextPlot','add');
axis(hAx, 'off','square')

%# draw circular path
line(D(:,1), D(:,2), 'Color',[.3 .3 .3], 'LineWidth',1);

%# initialize point
h = line('XData',D(1,1), 'YData',D(1,2), 'EraseMode','xor',  ...
        'Color','r', 'marker','.', 'MarkerSize',50);
%# init text
hTxt = text(0, 0, num2str(t(1)), 'FontSize',12, 'EraseMode','xor');

i=0;
while true
    i = rem(i+1,numel(t)) + 1;               %# circular increment
    set(h,'XData',D(i,1), 'YData',D(i,2))    %# update X/Y data
    set(hTxt,'String',num2str(t(i)))         %# update angle text
    drawnow                                  %# force refresh
    if ~ishandle(h), return; end             %# in case you close the figure
end

For a detailed explanation of the parameters used (EraseMode, Backingstore, DoubleBuffer, ..), refer to this animation guide

Answer 2

From the documentation for comet.m

t = 0:.01:2*pi;
x = cos(2*t).*(cos(t).^2);
y = sin(2*t).*(sin(t).^2);
comet(x,y);