Main Jacobian approximation
Jac_approx(f, x, nlevels = 5L)function to differentiate
evaluation point
depth of extrapolation. Default is 5.
Le, A., & Singleton, K. J. (2018). Small Package of Matlab Routines for
Estimation of Some Term Structure Models. EABCN Training School.
This function offers an independent R implementation that is informed
by the conceptual framework outlined in Le and Singleton (2018), but adapted to the
present modeling context.