module Newton:sig..end
val iter : float -> (float -> float) -> float -> floatiter dx f x0 is the Newton iterate obtained by applying one time
Newton's method to f and x0, using the infinitesimal dx.
It assumes the function f is defined for every real number.
val phi_iter : float -> floatphi_iter x0 is the Newton iterate following x0 and converging
the golden ratio phi.