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Partition-theoretic Frobenius-type limit formulas

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Abstract

Using partition generating function techniques, we prove q-series analogues of a formula of Frobenius generalizing Abel’s convergence theorem for complex power series. Frobenius’ result states that for \(|q|<1\), \(\lim _{q\rightarrow 1}(1-q)\sum _{n\ge 1} f(n) q^n \) is equal to the average value \(\lim _{N\rightarrow \infty }\) \(\frac{1}{N}\sum _{k=1}^{N}f(k)\) of the sequence \(\{f(n)\}\) as \(n\rightarrow \infty \), if the average value exists.

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Notes

  1. Proposition 1.2 is a statement of Frobenius’ theorem given in the second equation of [6], replacing \(a_n\) by f(n), and A by \(f_{{\text {avg}}}\); the condition that \(f_{{\text {avg}}}\) exists is equivalent to the Tauberian condition \(\sum _{k\le n}a_k\sim An\).

  2. We do not prove general q-summability theorems here. The property must be checked for a given f(n); general proofs of q-summability would be useful. We note here, as remarks, examples from previous works [7, 8, 10] proved by less general methods, as demonstrations that our general limit theorems are not vacuous.

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Acknowledgements

The author is indebted to George Andrews and Jeffrey Lagarias for discussions about analysis that influenced this paper, and to J. Lagarias for offering useful revisions; to Matthew R. Just, Ken Ono, Paul Pollack, A. V. Sills and Ian Wagner for conversations that advanced my work; and to the anonymous referee for suggestions that strengthened the final draft.

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Correspondence to Robert Schneider.

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Schneider, R. Partition-theoretic Frobenius-type limit formulas. Ramanujan J (2024). https://doi.org/10.1007/s11139-024-00835-4

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