This command calculates elements of the Jacobian matrix by means of centered finite difference quotients:
The evaluation of the Jacobian thus requires (2n+1) TOUGH2 simulations, where n is the number of parameters. The size of the perturbation dp can be controlled using command >>> PERTURB. Centered finite differences are more accurate than forward finite differences, but computationally twice as expensive (also see command >>> FORWARD).
>>> use CENTERED finite difference quotient
>>> PERTURBation factor is : 0.005 times the parameter value
>>> FORWARD (j) | >>> PERTURB