##  [Pole](/pole-1) 

 Definition

An isolated singularity a of a complex function f at which |f(z)|→∞ as z→a and for which there exists a positive integer m (the order) such that (z−a)^m f(z) extends to be analytic and nonzero at a.

 

 

 

 

 

 





## Principle

Principle

A pole of order m is characterized by a finite principal part in the Laurent expansion consisting of finitely many negative powers up to (z−a)^{-m}; multiplication by the appropriate power removes the singularity.

 

 

 

 

 





## Demonstration

Demonstration

Example: f(z)=1/(z−a)^m has a pole of exact order m at z=a; its Laurent series has terms c_{−m}(z−a)^{−m}+…+c_{−1}(z−a)^{−1} and no terms beyond that negative index.

 

 

 

 

## Misapplication

Misapplication

Calling any point where f becomes large a pole without checking isolatedness or finite principal-part order; essential singularities can produce unbounded growth without being poles.

 

 

 

 

 





## Consequence

Consequence

Poles are manageable singularities: residues can be computed, contour integrals evaluated, and local behavior classified; knowing order informs local mapping degree and local inversion properties.

 

 

 

 

## Reversal

Reversal

Opposite classifications are removable singularities (no negative principal part) and essential singularities (infinite negative tail) — the threefold classification for isolated singularities is exhaustive.

 

 

 

 

 





## Boundary

Boundary

Scope is isolated singularities of single-valued analytic functions; excludes branch points, accumulation of poles (natural boundaries), and non-isolated essential behavior.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Tension exists between high-order poles and nearby zeros of the numerator that may cancel order, and between poles and essential singularities when growth rates are compared — growth alone is not definitive.

 

 

 

 

 





## Synthesis

Synthesis

A pole is an isolated singularity with a finite-order algebraic blow-up captured by a finite negative Laurent principal part; it permits residue calculus and a clear local analytic normalization.