function M = chasemovie (robot, target, nframes)
%
% produces movie file from chase information
%
axis equal; axis ([-40 40 -40 40]);
M = moviein (nframes);
for k = 1:nframes
    hold on
    %
    % plot the trails in magenta and blue
    % 
    for j = max(1, k-5):k-1
        axis equal; axis ([-40 40 -40 40]); 
        plot (robot(j,1), robot(j,2), 'm.', target(j,1), target(j,2), 'b.');
    end    
    %
    % plot the new points in red and black
    % 
    plot (robot(k,1), robot(k,2), 'r.', target(k,1), target(k,2), 'k.');
    M(k) = getframe;
    hold off
    cla
end