function circle(x0,y0,radius)
 POINTS = 100;
 delta_phi = 2*pi/POINTS;
 phi=delta_phi:delta_phi:2*pi;
 x = x0*ones(1,POINTS)+cos(phi)*radius;
 y = y0*ones(1,POINTS)+sin(phi)*radius;
 plot(x,y);
end;
