Summability Calculus

Abstract

In this paper, we present the foundations of Summability Calculus, which places various established results in number theory, infinitesimal calculus, summability theory, asymptotic analysis, information theory, and the calculus of finite differences under a single simple umbrella. Using Summability Calculus, any given finite sum of the form $f(n) = \sum_{k=a}^n s_k\, g(k,n)$, where $s_k$ is an arbitrary periodic sequence, becomes immediately \emph{in analytic form}. Not only can we differentiate and integrate with respect to the bound $n$ without having to rely on an explicit analytic formula for the finite sum, but we can also deduce asymptotic expansions, accelerate convergence, assign natural values to divergent sums, and evaluate the finite sum for any $n\in\mathbb{C}$. This follows because the discrete definition of the simple finite sum $f(n) = \sum_{k=a}^n s_k\, g(k,n)$ embodies a \emph{unique natural} definition for all $n\in\mathbb{C}$. Throughout the paper, many established results are strengthened such as the Bohr-Mollerup theorem, Stirling's approximation, Glaisher's approximation, and the Shannon-Nyquist sampling theorem. In addition, many celebrated theorems are extended and generalized such as the Euler-Maclaurin summation formula and Boole's summation formula. Finally, we show that countless identities that have been proved throughout the past 300 years by different mathematicians using different approaches can actually be derived in an elementary straightforward manner using the rules of Summability Calculus.