Let $\mathcal{ H}$ be the class of all analytic self-maps of the open unit disk $\mathbb{ D}$. Denote by $H^n f(z)$ the $n$-th order hyperbolic derivative of $f\in \mathcal H$ at $z\in \mathbb{ D}$. For $z_0\in \mathbb{ D}$ and $\gamma = (\gamma_0, \gamma_1 , \ldots , \gamma_{ n-1}) \in { \mathbb D}^{ n}$, let ${ \mathcal H} (\gamma) = \{ f \in { \mathcal H} : f (z_0) = \gamma_0,H^1f (z_0) = \gamma_1,\ldots ,H^{ n-1}f (z_0) = \gamma_{ n-1} \}$. In this paper, we determine the variability region $V(z_0, \gamma ) = \{ f^{ (n)}(z_0) : f \in { \mathcal H} (\gamma) \}$, which can be called ``the generalized Schwarz-Pick Lemma of $n$-th derivative". We then apply the generalized Schwarz-Pick Lemma to establish a $n$-th order Dieudonn\'e's Lemma, which provides an explicit description of the variability region $\{ h^{ (n)}(z_0): h\in \mathcal{ H}, h(0)=0,h(z_0) =w_0, h'(z_0)=w_1,\ldots, h^{ (n-1)}(z_0)=w_{ n-1}\}$ for given $z_0$, $w_0$, $w_1,\dots,w_{ n-1}$. Moreover, we determine the form of all extremal functions.
Categories: math.CV
