Alphabeta Math
DefinitionDefinition: Literature-sourcedProof: Not applicablejudge pass (gpt-5.6-terra)audited 2026-08-26
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The residue of an isolated singularity

Definition

Let f have an isolated singularity at a. By Laurent expansion on an annulus, on every sufficiently small punctured disc about a it has a Laurent expansion

f(z)=∑n∈Zcn(z−a)n.

By Laurent coefficients are given by contour integrals and are unique, the coefficient c−1 is uniquely determined on that disc, and Laurent coefficients are independent of the intermediate radius shows that shrinking the disc does not change it. It is the residue of f at a, written

Res⁡(f,a):=c−1.

Remarks

The residue depends only on the singularity of f at a, not on which small punctured disc is used to write the Laurent series.

Depends on

Used by

Dependency tree · two levels

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Sources