Cauchy's integral formula

It expresses the value of a holomorphic function at an interior point as a contour integral of the function divided by (z - z_0) around a simple closed curve enclosing that point. It also yields integral formulas for all derivatives of the function.

f(z_0) = \frac{1}{2 \pi \mathrm{i}} \oint_{C} \frac{f(z)}{z - z_0} \, \mathrm{d}z

What the symbols mean

a holomorphic function of the complex variable z
a point inside the contour C
the complex variable of integration
a simple closed contour, positively oriented, enclosing z_0
the imaginary unit
the constant pi

About this formula

  • FieldMathematics
  • TopicComplex analysis
  • LevelUniversity
  • Also calledholomorphic function contour integral, value of holomorphic function from contour integral, derivatives of holomorphic function integral formula, Cauchy formula complex analysis
  • SourceWikidata Q913764

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