(bind-func ndiff_extrapolated
"numeric differentiation - extrapolated diff"
(lambda (f:[double,double]* x dx)
(/ (- (* 8.0 (- (f (+ x (/ dx 4.0)))
(f (- x (/ dx 4.0)))))
(- (f (+ x (/ dx 2.0)))
(f (- x (/ dx 2.0)))))
(* 3.0 dx))))