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Analytic Continuation 📂Complex Anaylsis

Analytic Continuation

Definition 1

For an analytic function f1:R1Cf_{1}: \mathscr{R}_{1} \to \mathbb{C} if there exists an analytic function f2:R2Cf_{2}: \mathscr{R}_{2} \to \mathbb{C} in R2C\mathscr{R}_{2} \subset \mathbb{C} that satisfies S:=R1R2f1(z)=f2(z),zS \mathscr{S} := \mathscr{R}_{1} \cap \mathscr{R}_{2} \ne \emptyset \\ f_{1} (z) = f_{2} (z) \qquad , z \in \mathscr{S} then f2f_{2} is called the Analytic Continuation of R2\mathscr{R}_{2} in f1f_{1}.

Explanation

Although this article is written in a complicated manner, if we read the definition carefully, it essentially means that in a certain complex domain S\mathscr{S}, f2f_{2} is simply an analytic function that can perfectly replace f1f_{1}. It is often called analytic extension because in many cases, we consider R1R2\mathscr{R}_{1} \subset \mathscr{R}_{2}.

The generalization of functions defined in the real numbers to the complex plane is like finding fCf_{\mathbb{C}} defined in R2=C\mathscr{R}_{2} = \mathbb{C} by properly generalizing the function fRf_{\mathbb{R}} we originally knew in R1=R\mathscr{R}_{1} = \mathbb{R}. The most straightforward examples include exponential functions exp()\exp ( \cdot ), gamma functions Γ()\Gamma ( \cdot ), and Riemann zeta functions ζ()\zeta (\cdot).


  1. Osborne (1999). Complex variables and their applications: p361. ↩︎