Abstract
Sums of the form \(\sum _{n\ge 0} (-1)^nq^{(n-1)n/2} x^n \) are called partial theta functions. In his lost notebook, Ramanujan recorded many identities for those functions. In 2003, Warnaar found an elegant formula for a sum of two partial theta functions. Subsequently, Andrews and Warnaar established a similar result for the product of two partial theta functions. In this note, I discuss the relation between the Andrews–Warnaar identity and the (1986) product formula due to Gasper and Rahman. I employ nonterminating extension of Sears–Carlitz transformation for \( _3\phi _2\) to provide a new elegant proof for a companion identity for the difference of two partial theta series. This difference formula first appeared in the work of Schilling–Warnaar (Conjugate Bailey pairs from configuration sums and fractional-level string functions to Bailey’s lemma. Contemporary mathematics, American Mathematical Society, Providence, vol 297, pp 227–255, 2002). Finally, I show that Schilling–Warnnar (2002) and Warnaar (Proc Lond Math Soc 87:363–395, 2003) formulas are, in fact, equivalent.
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Acknowledgements
My very special thanks are due to Heng Huat Chan for encouraging me to submit this old work for publication and for his kindness and time taken to retype this manuscript.
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Communicated by Heng Huat Chan.
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Research was supported in part by NSA Grant H98230-07-01-0011.
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Berkovich, A. On the Difference of Partial Theta Functions. Bull. Malays. Math. Sci. Soc. 44, 563–570 (2021). https://doi.org/10.1007/s40840-020-00961-4
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DOI: https://doi.org/10.1007/s40840-020-00961-4
Keywords
- Partial theta functions
- Lost notebook
- Jacobi’s triple product
- Transformation formula for well-poised \(_3\phi _2\)
- Quadratic transformations