+ int index;
+ double (* func_f) (struct lmm_variable *, double); /* f */
+ double (* func_fp) (struct lmm_variable *, double); /* f' */
+ double (* func_fpi) (struct lmm_variable *, double); /* (f')^{-1} */
+ double (* func_fpip) (struct lmm_variable *, double); /* ((f')^{-1})' */
+ double func_fi;