Multiple zeta function explained

In mathematics, the multiple zeta functions are generalizations of the Riemann zeta function, defined by

\zeta(s _{1,\ldots,s} _{k)} = \sum _{n _{1} > n _{2} > … > n _{k} > 0} (1)/(n ^{s _{1}} _{1} … n ^{s _{k}} _{k}) = \sum _{n _{1} > n _{2} > … > n _{k} > 0} \prod ^{k} _{i =1} (1)/(n ^{s _{i}} _{i}) ,

and converge when Re(s₁) + ... + Re(s_i) > i for all i. Like the Riemann zeta function, the multiple zeta functions can be analytically continued to be meromorphic functions (see, for example, Zhao (1999)). When s₁, ..., s_k are all positive integers (with s₁ > 1) these sums are often called multiple zeta values (MZVs) or Euler sums. These values can also be regarded as special values of the multiple polylogarithms.^{[1] [2]}

The k in the above definition is named the "depth" of a MZV, and the n = s₁ + ... + s_k is known as the "weight".^[3]

The standard shorthand for writing multiple zeta functions is to place repeating strings of the argument within braces and use a superscript to indicate the number of repetitions. For example,

\zeta( 2 , 1 , 2 , 1 , 3 ) = \zeta(\{ 2 , 1 \} ^{2,3).}

Definition

Multiple zeta functions arise as special cases of the multiple polylogarithms

Li _{s _{1,\ldots,s} _{d}} (\mu _{1,\ldots,\mu} _{d)} = \sum\limits _{k _{1> … >k} _{d>0}} (\mu ^{k _{1}} _{1} … \mu ^{k _{d}} _{d})/(k ^{s _{1}} _{1} … k ^{s _{d}} _{d})

which are generalizations of the polylogarithm functions. When all of the

\mu _{i} are n^th roots of unity and the s _{i} are all nonnegative integers, the values of the multiple polylogarithm are called colored multiple zeta values of level n . In particular, when n =2 , they are called Euler sums or alternating multiple zeta values, and when n =1 they are simply called multiple zeta values. Multiple zeta values are often written\zeta(s _{1,\ldots,s} _{d)} = \sum\limits _{k _{1} > … > k _{d} > 0} (1)/(k ^{s _{1}} _{1} … k ^{s _{d}} _{d})

and Euler sums are written

\zeta(s _{1,\ldots,s} _{d;\varepsilon} _{1,\ldots,\varepsilon} _{d)} = \sum\limits _{k _{1} > … > k _{d} > 0} (\varepsilon ^{k _{1}} _{1} … \varepsilon ^{k _{d}})/(k ^{s _{1}} _{1} … k ^{s _{d}} _{d})

where

\varepsilon _{i} = \pm 1 . Sometimes, authors will write a bar over an s _{i} corresponding to an \varepsilon _{i} equal to -1 , so for example\zeta(\overline{a},b) = \zeta(a,b; -1 , 1 ) .

Integral structure and identities

It was noticed by Kontsevich that it is possible to express colored multiple zeta values (and thus their special cases) as certain multivariable integrals. This result is often stated with the use of a convention for iterated integrals, wherein

\int ^{x} _{0} f _{1(t)} dt … f _{d(t)} dt = \int ^{x} _{0} f _{1(t} _{1)\left(\int} ^{t _{1}} ^{0} f _{2(t} _{2)\left(\int} ^{t _{2}} ^{0} … \left( \int ^{t _{d}} _{0} f _{d(t} _{d)} dt _{d\right)\right)dt} _{2\right)dt} _{1}

Using this convention, the result can be stated as follows:

Li _{s _{1,\ldots,s} _{d}} (\mu _{1,\ldots,\mu} _{d)} = \int ^{1} _{0} \left( (dt)/(t) \right) ^{s _{1-1}} (dt)/(a _{1-t}) … \left( (dt)/(t) \right) ^{s _{d-1}} (dt)/(a _{d-t}) where a _{j} = \prod\limits ^{j} _{i =1} \mu ^{-1} _{i} for j = 1 , 2 ,\ldots,d .

This result is extremely useful due to a well-known result regarding products of iterated integrals, namely that

\left(\int ^{x} _{0} f _{1(t)dt} … f _{n(t)} dt \right)\left(\int ^{x} _{0} f _{n+1} (t)dt … f _{m(t)} dt \right) = \sum\limits _{\sigma} _{n,m} }\int_0^x f_(t)\cdots f_(t) where ak{Sh} _{n,m} = \{\sigma \in S _{m} \mid \sigma( 1 )< … <\sigma(n), \sigma(n +1 )< … <\sigma(m)\} and S _{m} is the symmetric group on m symbols.

To utilize this in the context of multiple zeta values, define

X = \{a,b\} , X ^{*} to be the free monoid generated by X and ak{A} to be the free \Q -vector space generated by X ^{*} . ak{A} can be equipped with the shuffle product, turning it into an algebra. Then, the multiple zeta function can be viewed as an evaluation map, where we identify a = (dt)/(t) , b = (dt)/(1- t) , and define\zeta( w ) = \int ^{1} _{0} w for any w \in X ^{*} ,

which, by the aforementioned integral identity, makes

\zeta(a ^{s _{1-1}} b … a ^{s _{d-1}} b) = \zeta(s _{1,\ldots,s} _{d).}

Then, the integral identity on products gives

\zeta(w)\zeta(v) = \zeta(w ⧢ v).

Two parameters case

In the particular case of only two parameters we have (with s > 1 and n,&thinsp;m integers):^[4]

\zeta(s,t) = \sum _{n} (1)/(n ^{s} m ^{t}) = \sum ^{inf ty} _{n =2} (1)/(n ^{s}) \sum ^{n -1} _{m =1} (1)/(m ^{t}) = \sum ^{inf ty} _{n =1} (1)/((n +1 ) ^{s}) \sum ^{n} _{m =1} (1)/(m ^{t}) \zeta(s,t) = \sum ^{inf ty} _{n =1} (H _{n,t})/((n +1 ) ^{s}) where H _{n,t} are the generalized harmonic numbers.

Multiple zeta functions are known to satisfy what is known as MZV duality, the simplest case of which is the famous identity of Euler:

\sum ^{inf ty} _{n =1} (H _{n})/((n +1 ) ^{2}) = \zeta( 2 , 1 ) = \zeta( 3 ) = \sum ^{inf ty} _{n =1} (1)/(n ^{3}) ,

where H_n are the harmonic numbers.

Special values of double zeta functions, with s > 0 and even, t > 1 and odd, but s+t = 2N+1 (taking if necessary ζ(0) = 0):^[4]

\zeta(s,t) = \zeta(s)\zeta(t) + \tfrac{ 1 }{ 2 } [ \tbinom{s + t}{s} -1 ] \zeta(s + t) - \sum ^{N -1} _{r =1} [ \tbinom{ 2 r}{s -1 } + \tbinom{ 2 r}{t -1 } ] \zeta( 2 r +1 )\zeta(s + t -1-2 r)

s	t	approximate value	explicit formulae	OEIS
2	2	0.811742425283353643637002772406	\tfrac{ 3 }{ 4 }\zeta( 4 )
3	2	0.228810397603353759768746148942	3 \zeta( 2 )\zeta( 3 ) - \tfrac{ 11 }{ 2 }\zeta( 5 )
4	2	0.088483382454368714294327839086	\left (\zeta( 3 )\right ) ^{2-\tfrac{4}{3}\zeta(6)}
5	2	0.038575124342753255505925464373	5 \zeta( 2 )\zeta( 5 ) +2 \zeta( 3 )\zeta( 4 ) -11 \zeta( 7 )
6	2	0.017819740416835988362659530248
2	3	0.711566197550572432096973806086	\tfrac{ 9 }{ 2 }\zeta( 5 ) -2 \zeta( 2 )\zeta( 3 )
3	3	0.213798868224592547099583574508	\tfrac{ 1 }{ 2 }\left (\left (\zeta( 3 )\right ) ^{2} - \zeta( 6 )\right )
4	3	0.085159822534833651406806018872	17 \zeta( 7 ) -10 \zeta( 2 )\zeta( 5 )
5	3	0.037707672984847544011304782294	5 \zeta( 3 )\zeta( 5 ) - \tfrac{ 147 }{ 24 }\zeta( 8 ) - \tfrac{ 5 }{ 2 }\zeta( 6 , 2 )
2	4	0.674523914033968140491560608257	\tfrac{ 25 }{ 12 }\zeta( 6 ) - \left (\zeta( 3 )\right ) ^{2}
3	4	0.207505014615732095907807605495	10 \zeta( 2 )\zeta( 5 ) + \zeta( 3 )\zeta( 4 ) -18 \zeta( 7 )
4	4	0.083673113016495361614890436542	\tfrac{ 1 }{ 2 }\left (\left (\zeta( 4 )\right ) ^{2} - \zeta( 8 )\right )

Note that if s + t =2 p +2 we have p/ 3 irreducibles, i.e. these MZVs cannot be written as function of \zeta(a) only.

Three parameters case

In the particular case of only three parameters we have (with a > 1 and n, j,&thinsp;i integers):

\zeta(a,b,c) = \sum _{n} (1)/(n ^{a} j ^{b} i ^{c}) = \sum ^{inf ty} _{n =1} (1)/((n +2 ) ^{a}) \sum ^{n} _{j =1} (1)/((j +1 ) ^{b}) \sum ^{j} _{i =1} (1)/((i) ^{c}) = \sum ^{inf ty} _{n =1} (1)/((n +2 ) ^{a}) \sum ^{n} _{j =1} (H _{j,c})/((j +1 ) ^{b})

Euler reflection formula

The above MZVs satisfy the Euler reflection formula:

\zeta(a,b) + \zeta(b,a) = \zeta(a)\zeta(b) - \zeta(a + b) for a,b> 1

Using the shuffle relations, it is easy to prove that:^[5]

\zeta(a,b,c) + \zeta(a,c,b) + \zeta(b,a,c) + \zeta(b,c,a) + \zeta(c,a,b) + \zeta(c,b,a) = \zeta(a)\zeta(b)\zeta(c) +2 \zeta(a + b + c) - \zeta(a)\zeta(b + c) - \zeta(b)\zeta(a + c) - \zeta(c)\zeta(a + b) for a,b,c> 1

This function can be seen as a generalization of the reflection formulas.

Symmetric sums in terms of the zeta function

Let

S(i _{1,i} _{2, … ,i} _{k)} = \sum _{n _{1} \geq n _{2} \geq … n _{k} \geq 1} (1)/(n ^{i _{1}} _{1} n ^{i _{2}} _{2} … n ^{i _{k}} _{k}) , and for a partition \Pi = \{P _{1,} P _{2,} ... ,P _{l\}} of the set \{ 1 , 2 , ... ,k\} , let c(\Pi) = (\left|P _{1\right|-1)!(\left|P} _{2\right|-1)! … (\left|P} _{l\right|-1)!} . Also, given such a \Pi and a k-tuple i = \{i _{1,...,i} _{k\}} of exponents, define \prod ^{l} _{s =1} \zeta(\sum _{j \in P _{s}} i _{j)} .

The relations between the

\zeta and S are:S(i _{1,i} _{2)=\zeta(i} _{1,i} _{2)+\zeta(i} _{1+i} _{2)} and S(i _{1,i} _{2,i} _{3)=\zeta(i} _{1,i} _{2,i} _{3)+\zeta(i} _{1+i} _{2,i} _{3)+\zeta(i} _{1,i} _{2+i} _{3)+\zeta(i} _{1+i} _{2+i} _{3).}

Theorem 1 (Hoffman)

i _{1, … ,i} _{k} > 1 , , \sum _{{\sigma \in \Sigma _{k}} }S(i_, \dots, i_) = \sum_c(\Pi)\zeta(i,\Pi).

Proof. Assume the

i _{j} are all distinct. (There is no loss of generality, since we can take limits.) The left-hand side can be written as\sum _{\sigma} \sum _{n _{1\geq} n _{2} \geq … \geq n _{k} \geq 1} (1)/({n ^{i _{1}}) _{\sigma(1)} {n ^{i _{2}} }_ \cdots _ }. Now thinking on the symmetric

group

\Sigma _{k} as acting on k-tuple n = ( 1 , … ,k) of positive integers. A given k-tuple n = (n _{1, … ,n} _{k)} has an isotropy group\Sigma _{k(n)} and an associated partition Λ of ( 1 , 2 , … ,k) : Λ is the set of equivalence classes of the relation given by i \sim j iff n _{i=n} _{j} , and \Sigma _{k(n)} = \{\sigma \in \Sigma _{k} : \sigma(i) \sim \forall i\} . Now the term (1)/({n ^{i _{1}}) _{\sigma(1)} {n ^{i _{2}} }_ \cdots _} occurs on the left-hand side of \sum _{{\sigma \in \Sigma _{k}} }S(i_, \dots, i_) = \sum_c(\Pi)\zeta(i,\Pi) exactly \left| \Sigma _{k(n)} \right| times. It occurs on the right-hand side in those terms corresponding to partitions \Pi that are refinements of Λ : letting \succeq denote refinement, (1)/({n ^{i _{1}}) _{\sigma(1)} {n ^{i _{2}} }_ \cdots _} occurs \sum _{\Pi\succeqΛ} (\Pi) times. Thus, the conclusion will follow if \left| \Sigma _{k(n)} \right| = \sum _{\Pi\succeqΛ} c(\Pi) for any k-tuple n = \{n _{1, … ,n} _{k\}} and associated partition Λ .To see this, note that c(\Pi) counts the permutations having cycle type specified by \Pi : since any elements of \Sigma _{k(n)} has a unique cycle type specified by a partition that refines Λ , the result follows.^[6]

For

k =3 , the theorem says \sum _{{\sigma \in \Sigma _{3}} }S(i_,i_,i_) = \zeta(i_1)\zeta(i_2)\zeta(i_3)+\zeta(i_1+i_2)\zeta(i_3)+\zeta(i_1)\zeta(i_2+i_3)+\zeta(i_1+i_3)\zeta(i_2)+2\zeta(i_1+i_2+i_3)for i _{1,i} _{2,i} _{3>1} . This is the main result of.^[7]

Having

\zeta(i _{1,i} _{2, … ,i} _{k)=\sum} ^{n _{1>} n _{2> …} n _{k\geq1}} (1)/(n ^{i _{1}} _{1} n ^{i _{2}} _{2} … n ^{i _{k}} _{k}) . To state the analog of Theorem 1 for the \zeta's , we require one bit of notation. For a partition\Pi = \{P _{1, … ,P} _{l\}} of \{ 1 , 2 … ,k\} , let \tilde{c}(\Pi) = ( -1 ) ^{k-l} c(\Pi) .

Theorem 2 (Hoffman)

For any real

i _{1, … ,i} _{k>1} , \sum _{{\sigma \in \Sigma _{k}} }\zeta(i_, \dots, i_)=\sum_\tilde(\Pi)\zeta(i,\Pi).

Proof. We follow the same line of argument as in the preceding proof. The left-hand side is now

\sum _{\sigma} \sum _{n _{1} > n _{2} > … > n _{k} \geq 1} (1)/({n ^{i _{1}}) _{\sigma(1)} {n ^{i _{2}} }_ \cdots _ }, and a term (1)/(n ^{i _{1}} _{1} n ^{i _{2}} _{2} … n ^{i _{k}} _{k}) occurs on the left-hand since once if all the n _{i} are distinct, and not at all otherwise. Thus, it suffices to show \sum _{\Pi\succeqΛ} \tilde{c}(\Pi) = \begin{cases} 1 , if \left| Λ \right| = k \ 0 , otherwise . \end{cases} (1)

To prove this, note first that the sign of

\tilde{c}(\Pi) is positive if the permutations of cycle type \Pi are even, and negative if they are odd: thus, the left-hand side of (1) is the signed sum of the number of even and odd permutations in the isotropy group \Sigma _{k(n)} . But such an isotropy group has equal numbers of even and odd permutations unless it is trivial, i.e. unless the associated partition Λ is \{\{ 1 \},\{ 2 \}, … ,\{k\}\} .^[6]

The sum and duality conjectures^[6]

We first state the sum conjecture, which is due to C. Moen.^[8]

Sum conjecture (Hoffman). For positive integers k and n,

\sum _{i _{1+ … +i} _{k=n,} i _{1>1}} \zeta(i _{1, … ,i} _{k)} = \zeta(n) , where the sum is extended over k-tuples i _{1, … ,i} _{k} of positive integers with i _{1>1} .

Three remarks concerning this conjecture are in order. First, it implies

\sum _{i _{1+ … +i} _{k=n,} i _{1>1}} S(i _{1, … ,i} _{k)={n-1\choose} k -1 }\zeta(n) . Second, in the case k =2 it says that \zeta(n -1 , 1 ) + \zeta(n -2 , 2 ) + … + \zeta( 2 ,n -2 ) = \zeta(n) , or using the relation between the \zeta's and S's and Theorem 1, 2 S(n -1 , 1 ) = (n +1 )\zeta(n) - \sum ^{n -2} _{k =2} \zeta(k)\zeta(n - k). \tau on the set \Im of finite sequences of positive integers whose first element is greater than 1. Let \Tau be the set of strictly increasing finite sequences of positive integers, and let \Sigma : \Im → \Tau be the function that sends a sequence in \Im to its sequence of partial sums. If \Tau _{n} is the set of sequences in \Tau whose last element is at most n , we have two commuting involutions R _{n} and C _{n} on \Tau _{n} defined by R _{n(a} _{1,a} _{2,...,a} _{l)=(n+1-a} _{l,n+1-a} _{l-1} , ... ,n +1- a _{1)} and C _{n(a} _{1,...,a} _{l)} = complement of \{a _{1,...,a} _{l\}} in \{ 1 , 2 , ... ,n\} arranged in increasing order. The our definition of \tau is \tau(I) = \Sigma ^{-1} R _{nC} _{n\Sigma(I)} = \Sigma ^{-1} C _{nR} _{n\Sigma(I)} for I = (i _{1,i} _{2,...,i} _{k)} \in \Im with i _{1+ … +i} _{k=n} .

For example,

\tau( 3 , 4 , 1 ) = \Sigma ^{-1} C _{8R} _{8(3,7,8)} = \Sigma ^{-1} ( 3 , 4 , 5 , 7 , 8 ) = ( 3 , 1 , 1 , 2 , 1 ). We shall say the sequences (i _{1,...,i} _{k)} and \tau(i _{1,...,i} _{k)} are dual to each other, and refer to a sequence fixed by \tau as self-dual.^[6]

Duality conjecture (Hoffman). If

(h _{1,...,h} _{n-k} ) is dual to (i _{1,...,i} _{k)} , then \zeta(h _{1,...,h} _{n-k} ) = \zeta(i _{1,...,i} _{k)} .

This sum conjecture is also known as Sum Theorem, and it may be expressed as follows: the Riemann zeta value of an integer n ≥ 2 is equal to the sum of all the valid (i.e. with s₁ > 1) MZVs of the partitions of length k and weight n, with 1 ≤ k ≤ n − 1. In formula:^[3]

\sum _{\stackrel{s} _{1} + … + s _{k=n}{s} _{1>1}\zeta(s} _{1,} \ldots, s _{k)} = \zeta(n).

For example, with length k = 2 and weight n = 7:

\zeta( 6 , 1 ) + \zeta( 5 , 2 ) + \zeta( 4 , 3 ) + \zeta( 3 , 4 ) + \zeta( 2 , 5 ) = \zeta( 7 ).

Euler sum with all possible alternations of sign

The Euler sum with alternations of sign appears in studies of the non-alternating Euler sum.^[5]

Notation

\sum ^{inf ty} _{n =1} (H ^{(b)} _{n} ( -1 ) ^{(n+1)})/((n +1 ) ^{a}) = \zeta(\bar{a},b) with H ^{(b)} _{n} =+1+ (1)/(+ 2 ^{b}) (1)/(3 ^{b}) + … are the generalized harmonic numbers.\sum ^{inf ty} _{n =1} (\bar{H)/(_{n}) ^{(b)} }=\zeta(a,\bar) with \bar{H} ^{(b)} _{n} =-1+ (1)/(- 2 ^{b}) (1)/(3 ^{b}) + … \sum ^{inf ty} _{n =1} (\bar{H)/(_{n}) ^{(b)} ( -1 ) ^{(n+1)} }=\zeta(\bar,\bar) \sum ^{inf ty} _{n =1} (( -1 ) ^{n})/((n +2 ) ^{a}) \sum ^{inf ty} _{n =1} (\bar{H)/(_{n}) ^{(c)} ( -1 ) ^{(n+1)} } =\zeta(\bar,\bar,\bar) with \bar{H} ^{(c)} _{n} =-1+ (1)/(- 2 ^{c}) (1)/(3 ^{c}) + … \sum ^{inf ty} _{n =1} (( -1 ) ^{n})/((n +2 ) ^{a}) \sum ^{inf ty} _{n =1} (H ^{(c)} _{n})/((n +1 ) ^{b}) = \zeta(\bar{a},b,c) with H ^{(c)} _{n} =+1+ (1)/(+ 2 ^{c}) (1)/(3 ^{c}) + … \sum ^{inf ty} _{n =1} (1)/((n +2 ) ^{a}) \sum ^{inf ty} _{n =1} (H ^{(c)} _{n} ( -1 ) ^{(n+1)})/((n +1 ) ^{b}) = \zeta(a,\bar{b},c) \sum ^{inf ty} _{n =1} (1)/((n +2 ) ^{a}) \sum ^{inf ty} _{n =1} (\bar{H)/(_{n}) ^{(c)} }=\zeta(a,b,\bar) As a variant of the Dirichlet eta function we define\phi(s) = (1-2 ^{(s-1)})/(2 ^{(s-1)}) \zeta(s) with s> 1 \phi( 1 ) = -ln 2

Reflection formula

The reflection formula

\zeta(a,b) + \zeta(b,a) = \zeta(a)\zeta(b) - \zeta(a + b) can be generalized as follows:\zeta(a,\bar{b}) + \zeta(\bar{b},a) = \zeta(a)\phi(b) - \phi(a + b) \zeta(\bar{a},b) + \zeta(b,\bar{a}) = \zeta(b)\phi(a) - \phi(a + b) \zeta(\bar{a},\bar{b}) + \zeta(\bar{b},\bar{a}) = \phi(a)\phi(b) - \zeta(a + b) if a = b we have \zeta(\bar{a},\bar{a}) = \tfrac{ 1 }{ 2 } [ \phi ^{2(a)-\zeta(2a)]}

Other relations

Using the series definition it is easy to prove:

\zeta(a,b) + \zeta(a,\bar{b}) + \zeta(\bar{a},b) + \zeta(\bar{a},\bar{b}) = (\zeta(a,b))/(2 ^{(a+b-2)}) with a> 1 \zeta(a,b,c) + \zeta(a,b,\bar{c}) + \zeta(a,\bar{b},c) + \zeta(\bar{a},b,c) + \zeta(a,\bar{b},\bar{c}) + \zeta(\bar{a},b,\bar{c}) + \zeta(\bar{a},\bar{b},c) + \zeta(\bar{a},\bar{b},\bar{c}) = (\zeta(a,b,c))/(2 ^{(a+b+c-3)}) with a> 1 A further useful relation is:^[5] \zeta(a,b) + \zeta(\bar{a},\bar{b}) = \sum _{s>0} (a + b - s -1 )! [ (Z _{a(a+b-s,s)})/(+ (a - s)!(b -1 )!) (Z _{b(a+b-s,s)})/((b - s)!(a -1 )!) ] where Z _{a(s,t) = \zeta(s,t) + \zeta(\bar{s},t) - ([ \zeta(s,t) + \zeta(s + t) ])/(2 ^{(s-1)})} and Z _{b(s,t) = (\zeta(s,t))/(2 ^{(s-1)})}

Note that

s must be used for all value > 1 for which the argument of the factorials is \geqslant 0

Other results

For all positive integers

a,b, ... ,k :\sum ^{inf ty} _{n =2} \zeta(n,k) = \zeta(k +1 ) or more generally:\sum ^{inf ty} _{n =2} \zeta(n,a,b, ... ,k) = \zeta(a +1 ,b, ... ,k) \sum ^{inf ty} _{n =2} \zeta(n,\bar{k}) = - \phi(k +1 ) \sum ^{inf ty} _{n =2} \zeta(n,\bar{a},b) = \zeta(\overline{a +1 },b) \sum ^{inf ty} _{n =2} \zeta(n,a,\bar{b}) = \zeta(a +1 ,\bar{b}) \sum ^{inf ty} _{n =2} \zeta(n,\bar{a},\bar{b}) = \zeta(\overline{a +1 },\bar{b}) \lim _{k} \zeta(n,k) = \zeta(n) -1 1- \zeta( 2 ) + \zeta( 3 ) - \zeta( 4 ) + … = | (1)/(2) | \zeta(a,a) = \tfrac{ 1 }{ 2 } [ (\zeta(a)) ^{2} - \zeta( 2 a) ] \zeta(a,a,a) = \tfrac{ 1 }{ 6 }(\zeta(a)) ^{3} + \tfrac{ 1 }{ 3 }\zeta( 3 a) - \tfrac{ 1 }{ 2 }\zeta(a)\zeta( 2 a)

Mordell–Tornheim zeta values

The Mordell–Tornheim zeta function, introduced by who was motivated by the papers and, is defined by

\zeta _{MT,r} (s _{1,...,s} _{r;s} _{r+1} ) = \sum _{m _{1,...,m} _{r>0}} (1)/(m ^{s _{1}} _{1} … m ^{s _{r}} _{r} (m _{1+...+m} ^{s _{r+1}} ^{r)}) It is a special case of the Shintani zeta function.

References

• Tornheim . Leonard . Harmonic double series . 10.2307/2372034 . 0034860 . 1950 . . 0002-9327 . 72 . 2 . 303–314. 2372034 .
• Mordell . Louis J. . Louis Mordell. On the evaluation of some multiple series . 10.1112/jlms/s1-33.3.368 . 0100181 . 1958 . Journal of the London Mathematical Society . Second Series. 0024-6107 . 33 . 3 . 368–371.
  • Richard E.. Crandall. Joe P.. Buhler. On the evaluation of Euler Sums. 1994. Experimental Mathematics. 3. 4. 275. 1341720. 10.1080/10586458.1994.10504297.
• Jonathan M.. Borwein. Roland. Girgensohn. Evaluation of Triple Euler Sums. 1996. Electron. J. Comb.. 3. 1.
  1. R23
  . 10.37236/1247. 1401442. free. 1959.13/940394. free.
• Philippe. Flajolet. Bruno. Salvy. Euler Sums and contour integral representations. Exp. Math.. 1998. 7. 15–35. 10.1080/10586458.1998.10504356. 10.1.1.37.652.
• Zhao . Jianqiang. Analytic continuation of multiple zeta functions . 10.1090/S0002-9939-99-05398-8 . 1999 . Proceedings of the American Mathematical Society. 5 . 128 . 1275–1283. 1670846. free.
  • Olivier. Espinosa. Victor Hugo. Moll. Victor Hugo Moll . The evaluation of Tornheim double sums. 2008. math/0505647.
• Olivier. Espinosa. Victor Hugo. Moll. Victor Hugo Moll . The evaluation of Tornheim double sums II. Ramanujan J.. 2010. 22. 55–99. 2610609. 10.1007/s11139-009-9181-1. 0811.0557. 17055581.
• Borwein . J.M. . J.M. Borwein . Chan . O-Y.. Duality in tails of multiple zeta values . 2010. 10.1142/S1793042110003058. Int. J. Number Theory. 6. 3. 2652893. 501–514. 10.1.1.157.9158 .
• Ankur . Basu. On the evaluation of Tornheim sums and allied double sums. 2011. 10.1007/s11139-011-9302-5. Ramanujan J.. 26. 193–207. 2. 2853480. 120229489.

External links

• Web site: Jonathan. Borwein. Wadim. Zudilin. Lecture notes on the Multiple Zeta Function.
• Web site: Michael. Hoffman. Multiple zeta values. 2012.
• Book: Jianqiang . Zhao . 2016 . Multiple Zeta Functions, Multiple Polylogarithms and Their Special Values . 12 . World Scientific Publishing . 978-981-4689-39-7 . 10.1142/9634 . Series on Number Theory and its Applications .
• Web site: José Ignacio. Burgos Gil. Javier. Fresán. Multiple zeta values: from numbers to motives.

Notes and References

1. Standard relations of multiple polylogarithm values at roots of unity . Jianqiang . Zhao . Documenta Mathematica . 2010 . 15 . 1–34. 0707.1459 .
2. Book: Multiple Zeta Functions, Multiple Polylogarithms and Their Special Values . 12 . Jianqiang . Zhao . World Scientific Publishing . 2016. 978-981-4689-39-7 . 10.1142/9634 . Series on Number Theory and its Applications .
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