---
tag: 0PHN07KVQT
kind: concept
name: Residue
aliases: [residue-of-a-function]
msc: ["30E20"]
sources:
  - url: https://en.wikipedia.org/wiki/Residue_(complex_analysis)
    locator: lead section
same_as:
  wikidata: Q753375
  wikipedia: Residue (complex analysis)
---

## Summary

The residue of a function at an isolated singularity $c$ is the coefficient of $(z - c)^{-1}$ in its Laurent series, see the [[definition|0JFGKKWWFK]].
It is $\frac{1}{2\pi i}$ times the integral of the function around a small circle around $c$.