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Elliptic hypergeometric series

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Elliptic analog of hypergeometric series

In mathematics, an elliptic hypergeometric series is a series Σcn such that the ratio cn/cn−1 is an elliptic function of n, analogous to generalized hypergeometric series where the ratio is a rational function of n, and basic hypergeometric series where the ratio is a periodic function of the complex number n. They were introduced by Date-Jimbo-Kuniba-Miwa-Okado (1987) and Frenkel & Turaev (1997) in their study of elliptic 6-j symbols.

For surveys of elliptic hypergeometric series see Gasper & Rahman (2004), Spiridonov (2008) or Rosengren (2016).

Definitions

The q-Pochhammer symbol is defined by

( a ; q ) n = ∏ k = 0 n − 1 ( 1 − a q k ) = ( 1 − a ) ( 1 − a q ) ( 1 − a q 2 ) ⋯ ( 1 − a q n − 1 ) . {\displaystyle \displaystyle (a;q)_{n}=\prod _{k=0}^{n-1}(1-aq^{k})=(1-a)(1-aq)(1-aq^{2})\cdots (1-aq^{n-1}).}
( a 1 , a 2 , … , a m ; q ) n = ( a 1 ; q ) n ( a 2 ; q ) n … ( a m ; q ) n . {\displaystyle \displaystyle (a_{1},a_{2},\ldots ,a_{m};q)_{n}=(a_{1};q)_{n}(a_{2};q)_{n}\ldots (a_{m};q)_{n}.}

The modified Jacobi theta function with argument x and nome p is defined by

θ ( x ; p ) = ( x , p / x ; p ) ∞ {\displaystyle \displaystyle \theta (x;p)=(x,p/x;p)_{\infty }}
θ ( x 1 , . . . , x m ; p ) = θ ( x 1 ; p ) . . . θ ( x m ; p ) {\displaystyle \displaystyle \theta (x_{1},...,x_{m};p)=\theta (x_{1};p)...\theta (x_{m};p)}

The elliptic shifted factorial is defined by

( a ; q , p ) n = θ ( a ; p ) θ ( a q ; p ) . . . θ ( a q n − 1 ; p ) {\displaystyle \displaystyle (a;q,p)_{n}=\theta (a;p)\theta (aq;p)...\theta (aq^{n-1};p)}
( a 1 , . . . , a m ; q , p ) n = ( a 1 ; q , p ) n ⋯ ( a m ; q , p ) n {\displaystyle \displaystyle (a_{1},...,a_{m};q,p)_{n}=(a_{1};q,p)_{n}\cdots (a_{m};q,p)_{n}}

The theta hypergeometric series r+1Er is defined by

r + 1 E r ( a 1 , . . . a r + 1 ; b 1 , . . . , b r ; q , p ; z ) = ∑ n = 0 ∞ ( a 1 , . . . , a r + 1 ; q ; p ) n ( q , b 1 , . . . , b r ; q , p ) n z n {\displaystyle \displaystyle {}_{r+1}E_{r}(a_{1},...a_{r+1};b_{1},...,b_{r};q,p;z)=\sum _{n=0}^{\infty }{\frac {(a_{1},...,a_{r+1};q;p)_{n}}{(q,b_{1},...,b_{r};q,p)_{n}}}z^{n}}

The very well poised theta hypergeometric series r+1Vr is defined by

r + 1 V r ( a 1 ; a 6 , a 7 , . . . a r + 1 ; q , p ; z ) = ∑ n = 0 ∞ θ ( a 1 q 2 n ; p ) θ ( a 1 ; p ) ( a 1 , a 6 , a 7 , . . . , a r + 1 ; q ; p ) n ( q , a 1 q / a 6 , a 1 q / a 7 , . . . , a 1 q / a r + 1 ; q , p ) n ( q z ) n {\displaystyle \displaystyle {}_{r+1}V_{r}(a_{1};a_{6},a_{7},...a_{r+1};q,p;z)=\sum _{n=0}^{\infty }{\frac {\theta (a_{1}q^{2n};p)}{\theta (a_{1};p)}}{\frac {(a_{1},a_{6},a_{7},...,a_{r+1};q;p)_{n}}{(q,a_{1}q/a_{6},a_{1}q/a_{7},...,a_{1}q/a_{r+1};q,p)_{n}}}(qz)^{n}}

The bilateral theta hypergeometric series rGr is defined by

r G r ( a 1 , . . . a r ; b 1 , . . . , b r ; q , p ; z ) = ∑ n = − ∞ ∞ ( a 1 , . . . , a r ; q ; p ) n ( b 1 , . . . , b r ; q , p ) n z n {\displaystyle \displaystyle {}_{r}G_{r}(a_{1},...a_{r};b_{1},...,b_{r};q,p;z)=\sum _{n=-\infty }^{\infty }{\frac {(a_{1},...,a_{r};q;p)_{n}}{(b_{1},...,b_{r};q,p)_{n}}}z^{n}}

Definitions of additive elliptic hypergeometric series

The elliptic numbers are defined by

[ a ; σ , τ ] = θ 1 ( π σ a , e π i τ ) θ 1 ( π σ , e π i τ ) {\displaystyle ={\frac {\theta _{1}(\pi \sigma a,e^{\pi i\tau })}{\theta _{1}(\pi \sigma ,e^{\pi i\tau })}}}

where the Jacobi theta function is defined by

θ 1 ( x , q ) = ∑ n = − ∞ ∞ ( − 1 ) n q ( n + 1 / 2 ) 2 e ( 2 n + 1 ) i x {\displaystyle \theta _{1}(x,q)=\sum _{n=-\infty }^{\infty }(-1)^{n}q^{(n+1/2)^{2}}e^{(2n+1)ix}}

The additive elliptic shifted factorials are defined by

  • [ a ; σ , τ ] n = [ a ; σ , τ ] [ a + 1 ; σ , τ ] . . . [ a + n − 1 ; σ , τ ] {\displaystyle _{n}=...}
  • [ a 1 , . . . , a m ; σ , τ ] = [ a 1 ; σ , τ ] . . . [ a m ; σ , τ ] {\displaystyle =...}

The additive theta hypergeometric series r+1er is defined by

r + 1 e r ( a 1 , . . . a r + 1 ; b 1 , . . . , b r ; σ , τ ; z ) = ∑ n = 0 ∞ [ a 1 , . . . , a r + 1 ; σ ; τ ] n [ 1 , b 1 , . . . , b r ; σ , τ ] n z n {\displaystyle \displaystyle {}_{r+1}e_{r}(a_{1},...a_{r+1};b_{1},...,b_{r};\sigma ,\tau ;z)=\sum _{n=0}^{\infty }{\frac {_{n}}{_{n}}}z^{n}}

The additive very well poised theta hypergeometric series r+1vr is defined by

r + 1 v r ( a 1 ; a 6 , . . . a r + 1 ; σ , τ ; z ) = ∑ n = 0 ∞ [ a 1 + 2 n ; σ , τ ] [ a 1 ; σ , τ ] [ a 1 , a 6 , . . . , a r + 1 ; σ , τ ] n [ 1 , 1 + a 1 − a 6 , . . . , 1 + a 1 − a r + 1 ; σ , τ ] n z n {\displaystyle \displaystyle {}_{r+1}v_{r}(a_{1};a_{6},...a_{r+1};\sigma ,\tau ;z)=\sum _{n=0}^{\infty }{\frac {}{}}{\frac {_{n}}{_{n}}}z^{n}}

Further reading

  • Spiridonov, V. P. (2013). "Aspects of elliptic hypergeometric functions". In Berndt, Bruce C. (ed.). The Legacy of Srinivasa Ramanujan Proceedings of an International Conference in Celebration of the 125th Anniversary of Ramanujan's Birth; University of Delhi, 17-22 December 2012. Ramanujan Mathematical Society Lecture Notes Series. Vol. 20. Ramanujan Mathematical Society. pp. 347–361. arXiv:1307.2876. Bibcode:2013arXiv1307.2876S. ISBN 9789380416137.
  • Rosengren, Hjalmar (2016). "Elliptic Hypergeometric Functions". arXiv:1608.06161 .

References

Sequences and series
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Fibonacci spiral with square sizes up to 34.
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