todo

数学公式库--非常不错 The GNU Scientific Library (GSL) is a collection of routines for numerical computing. T

* Add an inline version of the iterate method for speed? Perhaps not,
the time taken for each iteration surely dominated by the convergence
test.

* Numerical derivatives? Maybe have a function to manufacture an fdf
from an f and optionally a df. (We'll need to approximate the
derivative if it is not provided; this is something which should be
done outside the root finding package.)