New test case (hard)

[HDembinski]

A challenging test case is the function y = np.log(1 + a1 * x + a2 * x**2) with $a1 = 2.0 \pm 0.2$ and $a2 = 1.0 \pm 0.1$ and correlation $\rho = -0.8$. Jacobi performs poorly in the divergent region near x = -1.