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Hurwitz zeta function

Table of contents: Definitions - Illustrations - Domain and range - Specific values - Series representations - Integral representations - Functional equations - Derivatives and differential equations - Euler-Maclaurin formula - Representation of other functions

Definitions

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Symbol: HurwitzZeta — ζ ⁣(s,a)\zeta\!\left(s, a\right) — Hurwitz zeta function

Illustrations

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Image: Plot of ζ ⁣(s,a)\zeta\!\left(s, a\right) on s∈[−25,11]s \in \left[-25, 11\right] for a∈{0.6,0.8,1.4}a \in \left\{0.6, 0.8, 1.4\right\}
583bf9
Image: X-ray of ζ ⁣(s,1+i2)\zeta\!\left(s, 1 + \frac{i}{2}\right) on s∈[−20,20]+[−20,20]is \in \left[-20, 20\right] + \left[-20, 20\right] i
0e2bcb
Image: X-ray of ζ ⁣(2+3i,a)\zeta\!\left(2 + 3 i, a\right) on a∈[−5,5]+[−5,5]ia \in \left[-5, 5\right] + \left[-5, 5\right] i

Domain and range

56dcbd
(s∈C∖{1}  and⁡  a∈C∖{0,−1,…})    ⟹    ζ ⁣(s,a)∈C\left(s \in \mathbb{C} \setminus \left\{1\right\} \;\mathbin{\operatorname{and}}\; a \in \mathbb{C} \setminus \{0, -1, \ldots\}\right) \;\implies\; \zeta\!\left(s, a\right) \in \mathbb{C}
ad269f
(s∈C  and⁡  Re⁡(s)<0  and⁡  a∈C)    ⟹    ζ ⁣(s,a)∈C\left(s \in \mathbb{C} \;\mathbin{\operatorname{and}}\; \operatorname{Re}(s) < 0 \;\mathbin{\operatorname{and}}\; a \in \mathbb{C}\right) \;\implies\; \zeta\!\left(s, a\right) \in \mathbb{C}
e7224b
(s∈R∖{1}  and⁡  a∈(0,∞))    ⟹    ζ ⁣(s,a)∈R\left(s \in \mathbb{R} \setminus \left\{1\right\} \;\mathbin{\operatorname{and}}\; a \in \left(0, \infty\right)\right) \;\implies\; \zeta\!\left(s, a\right) \in \mathbb{R}
b0f500
(s∈Z∖{1}  and⁡  a∈R∖{0,−1,…})    ⟹    ζ ⁣(s,a)∈R\left(s \in \mathbb{Z} \setminus \left\{1\right\} \;\mathbin{\operatorname{and}}\; a \in \mathbb{R} \setminus \{0, -1, \ldots\}\right) \;\implies\; \zeta\!\left(s, a\right) \in \mathbb{R}
cc523f
(s∈{0,−1,…}  and⁡  a∈Q)    ⟹    ζ ⁣(s,a)∈Q\left(s \in \{0, -1, \ldots\} \;\mathbin{\operatorname{and}}\; a \in \mathbb{Q}\right) \;\implies\; \zeta\!\left(s, a\right) \in \mathbb{Q}
ec2dd5
(s∈{0,−1,…}  and⁡  a∈R)    ⟹    ζ ⁣(s,a)∈R\left(s \in \{0, -1, \ldots\} \;\mathbin{\operatorname{and}}\; a \in \mathbb{R}\right) \;\implies\; \zeta\!\left(s, a\right) \in \mathbb{R}
a5980a
(s∈{0,−1,…}  and⁡  a∈C)    ⟹    ζ ⁣(s,a)∈C\left(s \in \{0, -1, \ldots\} \;\mathbin{\operatorname{and}}\; a \in \mathbb{C}\right) \;\implies\; \zeta\!\left(s, a\right) \in \mathbb{C}
d0b234
(s∈{1}  and⁡  a∈C∖{0,−1,…})    ⟹    ζ ⁣(s,a)∈{∞~}\left(s \in \left\{1\right\} \;\mathbin{\operatorname{and}}\; a \in \mathbb{C} \setminus \{0, -1, \ldots\}\right) \;\implies\; \zeta\!\left(s, a\right) \in \left\{{\tilde \infty}\right\}
c5d844
(s∈Z≥2  and⁡  a∈{0,−1,…})    ⟹    ζ ⁣(s,a)∈{∞~}\left(s \in \mathbb{Z}_{\ge 2} \;\mathbin{\operatorname{and}}\; a \in \{0, -1, \ldots\}\right) \;\implies\; \zeta\!\left(s, a\right) \in \left\{{\tilde \infty}\right\}

As a function of the argument

4bf3da
a∈C∖{0,−1,…}    ⟹    (ζ ⁣(s,a) is holomorphic on s∈C∖{1})a \in \mathbb{C} \setminus \{0, -1, \ldots\} \;\implies\; \left(\zeta\!\left(s, a\right) \text{ is holomorphic on } s \in \mathbb{C} \setminus \left\{1\right\}\right)
ea271f
a∈C∖{0,−1,…}    ⟹    (ζ ⁣(s,a) is meromorphic on s∈C)a \in \mathbb{C} \setminus \{0, -1, \ldots\} \;\implies\; \left(\zeta\!\left(s, a\right) \text{ is meromorphic on } s \in \mathbb{C}\right)
26418b
a∈C    ⟹    (ζ ⁣(s,a) is holomorphic on s∈{t:t∈C and⁡ Re⁡(t)<0})a \in \mathbb{C} \;\implies\; \left(\zeta\!\left(s, a\right) \text{ is holomorphic on } s \in \left\{ t : t \in \mathbb{C} \,\mathbin{\operatorname{and}}\, \operatorname{Re}(t) < 0 \right\}\right)

As a function of the parameter

93e149
s∈C∖{1}    ⟹    (ζ ⁣(s,a) is holomorphic on a∈C∖(−∞,0])s \in \mathbb{C} \setminus \left\{1\right\} \;\implies\; \left(\zeta\!\left(s, a\right) \text{ is holomorphic on } a \in \mathbb{C} \setminus \left(-\infty, 0\right]\right)
8c7cdb
s∈Z≥2    ⟹    (ζ ⁣(s,a) is holomorphic on a∈C∖{0,−1,…})s \in \mathbb{Z}_{\ge 2} \;\implies\; \left(\zeta\!\left(s, a\right) \text{ is holomorphic on } a \in \mathbb{C} \setminus \{0, -1, \ldots\}\right)
05c2dd
s∈Z≥2    ⟹    (ζ ⁣(s,a) is meromorphic on a∈C)s \in \mathbb{Z}_{\ge 2} \;\implies\; \left(\zeta\!\left(s, a\right) \text{ is meromorphic on } a \in \mathbb{C}\right)
f045b3
s∈{0,−1,…}    ⟹    (ζ ⁣(s,a) is holomorphic on a∈C)s \in \{0, -1, \ldots\} \;\implies\; \left(\zeta\!\left(s, a\right) \text{ is holomorphic on } a \in \mathbb{C}\right)

Specific values

af23f7
ζ ⁣(s,1)=ζ ⁣(s)\zeta\!\left(s, 1\right) = \zeta\!\left(s\right)
b721b4
ζ ⁣(s,2)=ζ ⁣(s)−1\zeta\!\left(s, 2\right) = \zeta\!\left(s\right) - 1
fc6fe0
ζ ⁣(s,3)=ζ ⁣(s)−1−12s\zeta\!\left(s, 3\right) = \zeta\!\left(s\right) - 1 - \frac{1}{{2}^{s}}
6e69fc
ζ ⁣(s,n)=ζ ⁣(s)−∑k=1n−11ks\zeta\!\left(s, n\right) = \zeta\!\left(s\right) - \sum_{k=1}^{n - 1} \frac{1}{{k}^{s}}
af7d3d
ζ ⁣(s,12)=(2s−1)ζ ⁣(s)\zeta\!\left(s, \frac{1}{2}\right) = \left({2}^{s} - 1\right) \zeta\!\left(s\right)
c6d6e2
ζ ⁣(s,32)=(2s−1)ζ ⁣(s)−2s\zeta\!\left(s, \frac{3}{2}\right) = \left({2}^{s} - 1\right) \zeta\!\left(s\right) - {2}^{s}
6c3523
ζ ⁣(s,12+n)=(2s−1)ζ ⁣(s)−2s∑k=0n−11(2k+1)s\zeta\!\left(s, \frac{1}{2} + n\right) = \left({2}^{s} - 1\right) \zeta\!\left(s\right) - {2}^{s} \sum_{k=0}^{n - 1} \frac{1}{{\left(2 k + 1\right)}^{s}}
8bbb6f
ζ ⁣(s,14)+ζ ⁣(s,34)=2s(2s−1)ζ ⁣(s)\zeta\!\left(s, \frac{1}{4}\right) + \zeta\!\left(s, \frac{3}{4}\right) = {2}^{s} \left({2}^{s} - 1\right) \zeta\!\left(s\right)
4d1f6b
ζ ⁣(s,16)+ζ ⁣(s,56)=(2s−1)(3s−1)ζ ⁣(s)\zeta\!\left(s, \frac{1}{6}\right) + \zeta\!\left(s, \frac{5}{6}\right) = \left({2}^{s} - 1\right) \left({3}^{s} - 1\right) \zeta\!\left(s\right)
575b8f
ζ ⁣(2,1)=π26\zeta\!\left(2, 1\right) = \frac{{\pi}^{2}}{6}
ac8d3c
ζ ⁣(2,2)=π26−1\zeta\!\left(2, 2\right) = \frac{{\pi}^{2}}{6} - 1
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ζ ⁣(3,1)=ζ ⁣(3)\zeta\!\left(3, 1\right) = \zeta\!\left(3\right)
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ζ ⁣(3,2)=ζ ⁣(3)−1\zeta\!\left(3, 2\right) = \zeta\!\left(3\right) - 1
2d4828
ζ ⁣(4,1)=π490\zeta\!\left(4, 1\right) = \frac{{\pi}^{4}}{90}
33690e
ζ ⁣(4,2)=π490−1\zeta\!\left(4, 2\right) = \frac{{\pi}^{4}}{90} - 1
868061
ζ ⁣(2,12)=π22\zeta\!\left(2, \frac{1}{2}\right) = \frac{{\pi}^{2}}{2}
9417f4
ζ ⁣(3,12)=7ζ ⁣(3)\zeta\!\left(3, \frac{1}{2}\right) = 7 \zeta\!\left(3\right)
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ζ ⁣(4,12)=π46\zeta\!\left(4, \frac{1}{2}\right) = \frac{{\pi}^{4}}{6}
3e82c3
ζ ⁣(2,14)=π2+8G\zeta\!\left(2, \frac{1}{4}\right) = {\pi}^{2} + 8 G
951f86
ζ ⁣(2,34)=π2−8G\zeta\!\left(2, \frac{3}{4}\right) = {\pi}^{2} - 8 G
eda0f3
ζ ⁣(3,14)=28ζ ⁣(3)+π3\zeta\!\left(3, \frac{1}{4}\right) = 28 \zeta\!\left(3\right) + {\pi}^{3}
b347d3
ζ ⁣(3,34)=28ζ ⁣(3)−π3\zeta\!\left(3, \frac{3}{4}\right) = 28 \zeta\!\left(3\right) - {\pi}^{3}
2fabeb
ζ ⁣(3,16)=91ζ ⁣(3)+23π3\zeta\!\left(3, \frac{1}{6}\right) = 91 \zeta\!\left(3\right) + 2 \sqrt{3} {\pi}^{3}
edad97
ζ ⁣(3,56)=91ζ ⁣(3)−23π3\zeta\!\left(3, \frac{5}{6}\right) = 91 \zeta\!\left(3\right) - 2 \sqrt{3} {\pi}^{3}
84196a
ζ ⁣(n,a)=(−1)n(n−1)!ψ(n−1) ⁣(a)\zeta\!\left(n, a\right) = \frac{{\left(-1\right)}^{n}}{\left(n - 1\right)!} \psi^{(n - 1)}\!\left(a\right)
532f31
ζ ⁣(1,a)=∞~\zeta\!\left(1, a\right) = {\tilde \infty}
5bdba2
ζ ⁣(−n,a)=−Bn+1 ⁣(a)n+1\zeta\!\left(-n, a\right) = -\frac{B_{n + 1}\!\left(a\right)}{n + 1}
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ζ ⁣(−n,0)=−Bn+1n+1\zeta\!\left(-n, 0\right) = -\frac{B_{n + 1}}{n + 1}
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ζ ⁣(0,a)=12−a\zeta\!\left(0, a\right) = \frac{1}{2} - a
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ζ ⁣(0,0)=12\zeta\!\left(0, 0\right) = \frac{1}{2}
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ζ ⁣(0,12)=0\zeta\!\left(0, \frac{1}{2}\right) = 0
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ζ ⁣(2,a)=a−2 3F2 ⁣(1,a,a,a+1,a+1,1)\zeta\!\left(2, a\right) = {a}^{-2} \,{}_3F_2\!\left(1, a, a, a + 1, a + 1, 1\right)

Series representations

Dirichlet series

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ζ ⁣(s,a)=∑n=0∞1(n+a)s\zeta\!\left(s, a\right) = \sum_{n=0}^{\infty} \frac{1}{{\left(n + a\right)}^{s}}
77e507
ζ(r) ⁣(s,a)=(−1)r∑n=0∞log⁡r ⁣(n+a)(n+a)s\zeta^{(r)}\!\left(s, a\right) = {\left(-1\right)}^{r} \sum_{n=0}^{\infty} \frac{\log^{r}\!\left(n + a\right)}{{\left(n + a\right)}^{s}}
0bd6aa
ζ ⁣(s,N)=∑n=N∞1ns\zeta\!\left(s, N\right) = \sum_{n=N}^{\infty} \frac{1}{{n}^{s}}

Laurent series

Related topic: Stieltjes constants
60c6da
ζ ⁣(s,a)=1s−1+∑n=0∞(−1)nn!γn ⁣(a)(s−1)n\zeta\!\left(s, a\right) = \frac{1}{s - 1} + \sum_{n=0}^{\infty} \frac{{\left(-1\right)}^{n}}{n !} \gamma_{n}\!\left(a\right) {\left(s - 1\right)}^{n}

Integral representations

1699a9
ζ ⁣(s,a)=π2(s−1)∫−∞∞(a−12+ix)1−scosh⁡2 ⁣(πx) dx\zeta\!\left(s, a\right) = \frac{\pi}{2 \left(s - 1\right)} \int_{-\infty}^{\infty} \frac{{\left(a - \frac{1}{2} + i x\right)}^{1 - s}}{\cosh^{2}\!\left(\pi x\right)} \, dx
498036
ζ ⁣(s,a)=1Γ(s)∫0∞xs−1e−ax1−e−x dx\zeta\!\left(s, a\right) = \frac{1}{\Gamma(s)} \int_{0}^{\infty} \frac{{x}^{s - 1} {e}^{-a x}}{1 - {e}^{-x}} \, dx

Functional equations

Recurrence relations

ed4f6f
ζ ⁣(s,a+1)=ζ ⁣(s,a)−1as\zeta\!\left(s, a + 1\right) = \zeta\!\left(s, a\right) - \frac{1}{{a}^{s}}
bed7ee
ζ ⁣(s,a+N)=ζ ⁣(s,a)−∑n=0N−11(n+a)s\zeta\!\left(s, a + N\right) = \zeta\!\left(s, a\right) - \sum_{n=0}^{N - 1} \frac{1}{{\left(n + a\right)}^{s}}
95e270
ζ(r) ⁣(s,a+N)=ζ(r) ⁣(s,a)+(−1)r+1∑k=0N−1log⁡r ⁣(a+k)(a+k)s\zeta^{(r)}\!\left(s, a + N\right) = \zeta^{(r)}\!\left(s, a\right) + {\left(-1\right)}^{r + 1} \sum_{k=0}^{N - 1} \frac{\log^{r}\!\left(a + k\right)}{{\left(a + k\right)}^{s}}

Multiplication formula

ba7f85
ζ ⁣(s,Na)=1Ns∑k=0N−1ζ ⁣(s,a+kN)\zeta\!\left(s, N a\right) = \frac{1}{{N}^{s}} \sum_{k=0}^{N - 1} \zeta\!\left(s, a + \frac{k}{N}\right)
ebc49c
ζ ⁣(s,a)=12s(ζ ⁣(s,a2)+ζ ⁣(s,a+12))\zeta\!\left(s, a\right) = \frac{1}{{2}^{s}} \left(\zeta\!\left(s, \frac{a}{2}\right) + \zeta\!\left(s, \frac{a + 1}{2}\right)\right)
7d9feb
ζ ⁣(s,a)=1Ns∑k=0N−1ζ ⁣(s,a+kN)\zeta\!\left(s, a\right) = \frac{1}{{N}^{s}} \sum_{k=0}^{N - 1} \zeta\!\left(s, \frac{a + k}{N}\right)

Reflection formula

69a1a9
ζ ⁣(1−s,pq)=2Γ(s)(2πq)s∑k=1qcos⁡ ⁣(πs2−2πkpq)ζ ⁣(s,kq)\zeta\!\left(1 - s, \frac{p}{q}\right) = \frac{2 \Gamma(s)}{{\left(2 \pi q\right)}^{s}} \sum_{k=1}^{q} \cos\!\left(\frac{\pi s}{2} - \frac{2 \pi k p}{q}\right) \zeta\!\left(s, \frac{k}{q}\right)

Derivatives and differential equations

Argument derivatives

3ba544
dds ζ ⁣(s,a)=ζ′ ⁣(s,a)\frac{d}{d s}\, \zeta\!\left(s, a\right) = \zeta'\!\left(s, a\right)
d0d03b
drdsrζ ⁣(s,a)=ζ(r) ⁣(s,a)\frac{d^{r}}{{d s}^{r}} \zeta\!\left(s, a\right) = \zeta^{(r)}\!\left(s, a\right)

Parameter derivatives

83065e
dda ζ ⁣(s,a)=−sζ ⁣(s+1,a)\frac{d}{d a}\, \zeta\!\left(s, a\right) = -s \zeta\!\left(s + 1, a\right)
40c3e2
drdarζ ⁣(s,a)=(1−s−r)rζ ⁣(s+r,a)\frac{d^{r}}{{d a}^{r}} \zeta\!\left(s, a\right) = \left(1 - s - r\right)_{r} \zeta\!\left(s + r, a\right)

Euler-Maclaurin formula

d25d10
ζ ⁣(s,a)=∑k=0N−11(a+k)s+(a+N)1−ss−1+1(a+N)s(12+∑k=1MB2k(2k)!(s)2k−1(a+N)2k−1)−∫N∞B2M ⁣(t−⌊t⌋)(2M)!(s)2M(a+t)s+2M dt\zeta\!\left(s, a\right) = \sum_{k=0}^{N - 1} \frac{1}{{\left(a + k\right)}^{s}} + \frac{{\left(a + N\right)}^{1 - s}}{s - 1} + \frac{1}{{\left(a + N\right)}^{s}} \left(\frac{1}{2} + \sum_{k=1}^{M} \frac{B_{2 k}}{\left(2 k\right)!} \frac{\left(s\right)_{2 k - 1}}{{\left(a + N\right)}^{2 k - 1}}\right) - \int_{N}^{\infty} \frac{B_{2 M}\!\left(t - \left\lfloor t \right\rfloor\right)}{\left(2 M\right)!} \frac{\left(s\right)_{2 M}}{{\left(a + t\right)}^{s + 2 M}} \, dt

Representation of other functions

Riemann zeta function

Related topic: Riemann zeta function
febdd2
ζ ⁣(s)=ζ ⁣(s,1)\zeta\!\left(s\right) = \zeta\!\left(s, 1\right)

Bernoulli polynomials

Related topic: Bernoulli numbers and polynomials
4228cd
Bn ⁣(z)=−nζ ⁣(1−n,z)B_{n}\!\left(z\right) = -n \zeta\!\left(1 - n, z\right)

Gamma and related functions

Related topics: Digamma function, Barnes G-function
53026a
Γ(z)=2πexp⁡ ⁣(ζ′ ⁣(0,z))\Gamma(z) = \sqrt{2 \pi} \exp\!\left(\zeta'\!\left(0, z\right)\right)
f3b870
log⁡Γ(z)=ζ′ ⁣(0,z)+log⁡ ⁣(2π)2\log \Gamma(z) = \zeta'\!\left(0, z\right) + \frac{\log\!\left(2 \pi\right)}{2}
693e0e
ψ ⁣(z)=lim⁡s→1[1s−1−ζ ⁣(s,z)]\psi\!\left(z\right) = \lim_{s \to 1} \left[\frac{1}{s - 1} - \zeta\!\left(s, z\right)\right]
bba4ec
ψ(m) ⁣(z)=(−1)m+1m!ζ ⁣(m+1,z)\psi^{(m)}\!\left(z\right) = {\left(-1\right)}^{m + 1} m ! \zeta\!\left(m + 1, z\right)
e05807
log⁡G(z)=(z−1)log⁡Γ(z)−ζ′ ⁣(−1,z)+ζ′(−1)\log G(z) = \left(z - 1\right) \log \Gamma(z) - \zeta'\!\left(-1, z\right) + \zeta'(-1)

Dirichlet L-functions

Related topic: Dirichlet L-functions
c31c10
L ⁣(s,χ)=1qs∑k=1qχ(k)ζ ⁣(s,kq)L\!\left(s, \chi\right) = \frac{1}{{q}^{s}} \sum_{k=1}^{q} \chi(k) \zeta\!\left(s, \frac{k}{q}\right)
4c3678
ζ ⁣(s,kq)=qsφ(q)∑χ∈Gqχ(k)‾L ⁣(s,χ)\zeta\!\left(s, \frac{k}{q}\right) = \frac{{q}^{s}}{\varphi(q)} \sum_{\chi \in G_{q}} \overline{\chi(k)} L\!\left(s, \chi\right)

Polylogarithms

52ea5f
Li⁡s ⁣(z)=Γ ⁣(1−s)(2π)1−s(i1−sζ ⁣(1−s,12+log⁡ ⁣(−z)2πi)+is−1ζ ⁣(1−s,12−log⁡ ⁣(−z)2πi))\operatorname{Li}_{s}\!\left(z\right) = \frac{\Gamma\!\left(1 - s\right)}{{\left(2 \pi\right)}^{1 - s}} \left({i}^{1 - s} \zeta\!\left(1 - s, \frac{1}{2} + \frac{\log\!\left(-z\right)}{2 \pi i}\right) + {i}^{s - 1} \zeta\!\left(1 - s, \frac{1}{2} - \frac{\log\!\left(-z\right)}{2 \pi i}\right)\right)

Copyright (C) Fredrik Johansson and contributors. Fungrim is provided under the MIT license. The source code is on GitHub.

2021-03-15 19:12:00.328586 UTC