[PL] Perturb xdot in central differences Jacobian.
From \dot{x} \approx (x - x_0)/dt
with a perturbation of
\hat{x} = x + \epsilon
it follows that for consistency \dot{x}
has to be perturbed with \epsilon/dt
to keep the x_0
unchanged.
From \dot{x} \approx (x - x_0)/dt
with a perturbation of
\hat{x} = x + \epsilon
it follows that for consistency \dot{x}
has to be perturbed with \epsilon/dt
to keep the x_0
unchanged.