English

Growth of recurrences with mixed multifold convolutions

Combinatorics 2024-10-25 v1

Abstract

Generalizing some popular sequences like Catalan's number, Schr\"oder's number, etc, we consider the sequence sns_n with s0=1s_0=1 and for n1n\ge 1, \begin{multline*} s_n=\sum_{x_1+\dots+x_{\ell_1}=n-1} \kappa_1 s_{x_1}\dots s_{x_{\ell_1}} + \dots +\sum_{x_1+\dots+x_{\ell_{t'}}=n-1} \kappa_{t'} s_{x_1}\dots s_{x_{\ell_{t'}}}+\\ \max_{x_1+\dots+x_{\ell_{t'+1}}=n-1} \kappa_{t'+1} s_{x_1}\dots s_{x_{\ell_{t'+1}}} + \dots + \max_{x_1+\dots+x_{\ell_t}=n-1} \kappa_t s_{x_1}\dots s_{x_{\ell_t}}, \end{multline*} where xix_i are nonnegative integers, 1,,t\ell_1,\dots,\ell_t are positive integers, and κ1,,κt\kappa_1,\dots,\kappa_t are positive reals. We show that it is possible to compute the growth rate λ\lambda of sns_n to any precision. In particular, for every n2n\ge 2, κL(n1)s1snnλ318log3+2logs1L2κn3logn+12log3+logs1L2κsnn, \sqrt[n]{\frac{\kappa^*}{\mathcal L(n-1) s_1} s_n} \le \lambda \le \sqrt[n]{3^{18\log 3 + 2\log\frac{s_1\mathcal L^2}{\kappa^*}} n^{3\log n + 12\log 3 + \log\frac{s_1\mathcal L^2}{\kappa^*}} s_n}, where L=maxii\mathcal L=\max_i \ell_i and κ=κi\kappa^*=\kappa_i for some ii with i2\ell_i\ge 2, and the logarithm has the base L+1L\frac{\mathcal L+1}{\mathcal L}. The constants in the inequalities are not very well optimized and serve mostly as a proof of concept with the ratio of the upper bound and the lower bound converging to 11 as nn goes to infinity.

Keywords

Cite

@article{arxiv.2410.18534,
  title  = {Growth of recurrences with mixed multifold convolutions},
  author = {Vuong Bui},
  journal= {arXiv preprint arXiv:2410.18534},
  year   = {2024}
}

Comments

8 pages; comments are welcome