Question 23.6: The van der Pol equation is a model of an electronic circuit...

The van der Pol equation is a model of an electronic circuit that arose back in the days of vacuum tubes,
\frac{d^2 y_1}{d t^2}-\mu\left(1-y_1^2\right) \frac{d y_1}{d t}+y_1=0        (E23.6.1)
The solution to this equation becomes progressively stiffer as μ gets large. Given the initial conditions, y_1(0) = dy_1/dt = 1, use MATLAB to solve the following two cases: (a) for μ = 1, use ode45 to solve from t = 0 to 20; and (b) for μ = 1000, use ode23s to solve from t = 0 to 6000.