clear; clc; close all 
x1=3.14; 
p1=-0.0001; 
dt=0.025; 

% hl=plot(x1,p1,'o');
xx=[0 sin(x1)];
yy=[0 -cos(x1)];
hl=plot(xx,yy,'-o');
axis([-pi pi -pi pi]); 
set(hl,'Color','r');
grid on;
%pause; 
% hold on
while 1
x2=x1+p1*dt;
p2=p1-sin(x2)*dt;
if x2> pi
x2=x2-2*pi;
end
if x2< -pi
x2=x2+2*pi;
end
%set(hl,'XData',x2,'YData',p2);
% plot(x2,p2,'o')
xx=[0 sin(x2)];
yy=[0 -cos(x2)];
% hl=plot(xx,yy,'-o');
% axis([-pi pi -pi pi]); 
set(hl,'XData',xx,'YData',yy);
x1=x2;p1=p2;
pause(0.01)
end