GV

GeezerVison

The World Wide Web, restored to 800 pixels of glory.

Home|About|Gaming cabinet|Archives|How it works|Starter sites

On this site

  • Algebra
  • Applied Mathematics
  • Calculus and Analysis
  • Discrete Mathematics
  • Foundations of Mathematics
  • Geometry
  • History and Terminology
  • Number Theory
  • Probability and Statistics
  • Recreational Mathematics
  • Topology
  • Alphabetical Index
  • Random Entry
  • New in MathWorld

This view

  • Original page
  • New address

GeezerVison is showing mathworld.wolfram.com — Abel's Convergence Theorem -- from Wolfram MathWorld

Search

Abel's Convergence Theorem


Abel's convergence theorem extends the uniform convergence of a power series and the continuity of its sum to a convergent boundary point. Given a Taylor series

 f(z)=sum_(n=0)^inftyC_nz^n=sum_(n=0)^inftyC_nr^ne^(intheta),
(1)

where the complex number z has been written in the polar form z=re^(itheta), examine the real and imaginary parts

 u(r,theta)=sum_(n=0)^inftyC_nr^ncos(ntheta)
(2)
 v(r,theta)=sum_(n=0)^inftyC_nr^nsin(ntheta).
(3)

Abel's theorem states that, if u(1,theta) and v(1,theta) are convergent, then

 u(1,theta)+iv(1,theta)=lim_(r->1)f(re^(itheta)).
(4)

Stated in words, Abel's theorem guarantees that, if a real power series converges for some positive value of the argument, the domain of uniform convergence extends at least up to and including this point. Furthermore, the continuity of the sum function extends at least up to and including this point.


See also

Abel-Regularized Sum, Power Series, Uniform Convergence

Explore with Wolfram|Alpha

WolframAlpha

More things to try:

  • 7 rows of Pascal's triangle
  • conical spiral
  • jordan normal form calculator

References

Arfken, G. Mathematical Methods for Physicists, 3rd ed. Orlando, FL: Academic Press, p. 773, 1985.

Referenced on Wolfram|Alpha

Abel's Convergence Theorem

Cite this as:

Weisstein, Eric W. "Abel's Convergence Theorem." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/AbelsConvergenceTheorem.html

Subject classifications

You are visitor 01402520 — GeezerVison does not store the pages you look up.
Best viewed with Netscape Navigator 4.7 or Internet Explorer 6 at 800×600. No cookies required.