function dx = fnode4(t,x)

dx = zeros(2,1);

if t<50
    dx(1) = x(1) - x(1)^3/3-x(2)-0.5;
else
    dx(1) = x(1) - x(1)^3/3-x(2);
end

dx(2) = 0.08*(x(1)+0.7-0.8*x(2));