Conditional convergence

Definition

Conditional convergence refers to a specific type of convergence of infinite series where the series converges when the terms are taken in their original order, but diverges if the absolute values of the terms are considered. This concept highlights an interesting distinction in series behavior, indicating that rearranging the terms can lead to different outcomes regarding convergence.

5 Must Know Facts For Your Next Test

1. Conditional convergence occurs in series where the sum of the absolute values diverges, but the original series converges.
2. An example of a conditionally convergent series is the alternating harmonic series, which converges to ln(2).
3. Rearranging the terms of a conditionally convergent series can lead to different sums or even divergence, as per the Riemann series theorem.
4. In contrast, absolutely convergent series remain convergent regardless of how their terms are rearranged.
5. Identifying conditional convergence often involves using tests for convergence, such as the Alternating Series Test or the Ratio Test.

Review Questions

• How does conditional convergence differ from absolute convergence?
  • Conditional convergence differs from absolute convergence in that a conditionally convergent series converges when taken in its original order, but its corresponding series of absolute values diverges. In contrast, an absolutely convergent series guarantees convergence regardless of how the terms are arranged. This distinction is crucial because it affects how we handle series in calculations and proofs, especially when considering term rearrangements.
• What implications does the Riemann series theorem have on conditionally convergent series?
  • The Riemann series theorem states that any conditionally convergent series can be rearranged to converge to any real number or even to diverge completely. This means that while a conditionally convergent series may have a specific sum when its terms are ordered in one way, altering that order can change the outcome dramatically. This property emphasizes the sensitivity of conditional convergence to term arrangement and is essential for understanding its implications in analysis.
• Evaluate the significance of the alternating harmonic series as an example of conditional convergence, discussing its properties and applications.
  • The alternating harmonic series is significant because it serves as a classic example of conditional convergence; it converges to ln(2) despite the divergence of the harmonic series formed by its absolute values. This characteristic illustrates key properties of alternating series and showcases how they can converge even when their absolute counterparts do not. Its application extends into various areas of mathematical analysis, where understanding conditional convergence is essential for evaluating more complex functions and series.

Related terms

absolute convergence: A series is said to converge absolutely if the series formed by taking the absolute values of its terms converges.

Riemann series theorem: A theorem that states that any conditionally convergent series can be rearranged to converge to any real number or even diverge.

alternating series: A type of series where the terms alternate in sign, often used in demonstrating conditional convergence.