nonlinear-pendulum

This is, for practice, a non-linear pendulum PDE solver. We are discretizing

\theta''(t)= - sin(\theta(t))

to get

(1/h^2) (\theta_(i-1) - 2 \theta_i + \theta_(i+1)) + sin(\theta_i) = 0

which is nonlinear. I'll use a Newton update step.