function dy=wang(t,y)
I=0.2;
eta=0.02;
gamma=6.0;
beta=0.1;
dy=zeros(2,1);
dy(1)=3*y(1)-y(1)^3+2-y(2)+I;
dy(2)=eta*(gamma*(1+tanh(y(1)/beta))-y(2));
