Infinite series and absolute convergence
A series converges through its partial sums.
Key knowledge
The series Σaₙ converges when its partial sums converge to a finite real limit. Absolute convergence, Σ|aₙ|<∞, implies convergence; aₙ→0 alone does not suffice.
Conditions and scope
- Here terms are real and the index order is fixed.
- Conditionally convergent series cannot be freely rearranged.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Definition 4.1 and Proposition 4.17: partial sums and absolute convergence.
2026-10-10 · Partial-sum definition and absolute-convergence implication.
Related reference entries
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Showing 1–14 of 14 relationships
Scientific relationships · 14 / 14
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- Uses definition
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Linked statements
- The series Σaₙ converges when its partial sums converge to a finite real limit. Absolute convergence, Σ|aₙ|<∞, implies convergence; aₙ→0 alone does not suffice.
- Uses definition
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Linked statements
- For a constant real n×n matrix A, x′=Ax with x(0)=x₀ has the unique global solution x(t)=eᵗᴬx₀, where eᵗᴬ=Σₖ₌₀∞ tᵏAᵏ/k! converges for every real t.
- Uses definition
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Linked statements
- If real functions fₙ on one set A satisfy |fₙ(x)|≤Mₙ for all x∈A, with Mₙ≥0 and ΣMₙ<∞, then Σfₙ converges uniformly and absolutely on A. Its uniform tail is bounded by the corresponding majorant tail.
- Uses definition
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Linked statements
- For positive continuous decreasing f on [1,∞), Σₙ₌₁∞f(n) and ∫₁∞f(x)dx converge or diverge together. Consequently Σn⁻ᵖ converges exactly when p>1.
- Uses definition
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Linked statements
- If bₙ≥0 decreases to zero, Σ(−1)ⁿbₙ converges; the absolute error after N terms is at most the next omitted magnitude b_(N+1).
- Uses definition
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Linked statements
- A holomorphic function has a convergent Taylor expansion within a disk free of singularities. On an annulus about z₀ it has a unique Laurent expansion Σₙ∈Z aₙ(z−z₀)ⁿ; its negative-power terms form the principal part.
- Uses definition
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Linked statements
- For a 2L-periodic piecewise smooth real f, aₙ=L⁻¹∫₋ᴸᴸf(t)cos(nπt/L)dt and bₙ=L⁻¹∫₋ᴸᴸf(t)sin(nπt/L)dt. The series a₀/2+Σₙ≥₁[aₙcos(nπt/L)+bₙsin(nπt/L)] converges to the mean of the two one-sided limits.
- Uses definition
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Linked statements
- If operation i changes state Dᵢ₋₁ to Dᵢ, define ĉᵢ=cᵢ+Φ(Dᵢ)−Φ(Dᵢ₋₁). Summing telescopes to Σcᵢ=Σĉᵢ+Φ(D₀)−Φ(Dₙ); with Φ(D₀)=0 and nonnegative final potential, amortized totals bound actual totals.
- Uses definition
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Linked statements
- For eventually nonnegative terms aₙ≤bₙ, convergence of Σbₙ implies convergence of Σaₙ; divergence of Σaₙ implies divergence of Σbₙ. If bₙ>0 and aₙ/bₙ→L with 0<L<∞, the two series converge or diverge together.
- Uses definition
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Linked statements
- If |aₙ₊₁/aₙ|→ρ, or |aₙ|¹⁄ⁿ→ρ, then Σaₙ converges absolutely for ρ<1 and diverges for ρ>1. At ρ=1 either behavior is possible.
- Uses definition
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Linked statements
- For T(n)=aT(n/b)+f(n), T(1)=Θ(1), let q=log_b a. If f=O(n^(q−ε)), then T=Θ(n^q). If f=Θ(n^q(log n)^k), then T=Θ(n^q(log n)^(k+1)). If f=Ω(n^(q+ε)) and af(n/b)≤c f(n) eventually, then T=Θ(f(n)).
- Uses definition
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Linked statements
- For a complex 2π-periodic Riemann-integrable f, cₙ=(2π)⁻¹∫₋π^πf(x)e⁻ⁱⁿˣdx and s_N=Σ|n|≤N cₙeⁱⁿˣ satisfy ∫|f−s_N|²→0. Parseval gives (2π)⁻¹∫₋π^π|f|²=Σₙ∈Z|cₙ|². This is mean-square convergence, which does not assert pointwise convergence everywhere.
- Uses definition
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Linked statements
- If Nʳ=0 and A=λI+N, then eᵗᴬ=e^(λt)Σₖ₌₀ʳ⁻¹tᵏNᵏ/k!. For a size-r Jordan block J=λI+N with ones on the first superdiagonal, Nʳ=0 and its k-th superdiagonal in eᵗᴶ is e^(λt)tᵏ/k!. Similarity transports this formula: e^(tPJP⁻¹)=PeᵗᴶP⁻¹.
- Related to
Relationship sources · 2
- 18.785 (Fall 2025), Lecture 16: zeta and prime numbers ↗
- 18.785 (Fall 2025), Lecture 18: Dirichlet L-functions ↗
Linked statements
- The prime-counting function satisfies pi(x)~x/log x. For fixed q and gcd(a,q)=1, primes p≤x with p congruent to a modulo q have count asymptotic to Li(x)/phi(q). Nonvanishing at s=1 of the relevant nonprincipal Dirichlet L-functions underpins the progression result. A fixed-modulus asymptotic is not a uniform numerical guarantee when q grows with x.
Asymptotic statements concern limiting behavior rather than finite equality.
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