x=[1:0.1:40*pi];
y=sin(5*x)*sin(0.1*x).*cos(2*x)
plot(x,y)
xlabel('time); ylabel('intensity');
tic; figure(); maxvalue = 100; 
set(gca,'XLim',[0 maxvalue]); set(gca,'YLim',[0 1]);
hold on; plot([0 maxvalue],[.5 .5])
for k=1:maxvalue value = rand;
  if value<0.5 disp('Lower half'); else disp('Upper half'); end
plot(k,value,'rx'); pause(0.02);
  end
hold off
toc
tic; t = 0:0.01:2*pi; x = 4 * cos(3*t); y = 4 * cos(4*t+pi/2);
figure; hold on; for k=1:length(x) plot(x(k),y(k),'r.'); pause(0.001); end