**keyword:**

`FINITE-DIFFERENCE-GRADIENTS`

The user is assumed to have provided analytic expressions for the
values
of the nonlinear element functions in the SEIF file.
The specification of analytic first derivatives is optional, but
recommended whenever possible.
If the user is unable to provide analytic first derivatives
of the nonlinear element functions, the
derivatives will be approximated
by finite differences whenever the
`FINITE-DIFFERENCE-GRADIENTS` keyword is specified. The user should
note, however, that the accuracy of the solution obtained by
*LANCELOT* may be compromised if finite-difference approximations
are used.