function fn = ffoucault(t,y)
    l=20; k2=9.8/l; psi=pi/4; omega=7.29*1.e-06;
    [n,m] = size(y); fn = zeros(n,m);
    fn(1)=y(3); fn(2)=y(4);
    fn(3)=2*omega*sin(psi)*y(4)-k2*y(1);
    fn(4)=-2*omega*sin(psi)*y(3)-k2*y(2);
return