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Theoretical Backgrounds of Applied Discrete Mathematics
Bernoulli's discrete periodic functions
M. S. Bespalov Vladimir State University named after Alexander and Nikolay Stoletovs, Vladimir, Russia
Abstract:
This paper is a survey of known and some new properties of the discrete periodic Bernoulli functions
$b_n(j)$
of order
$n$ introduced by V. N. Malozemov
and viewed as elements $x=x(0)x(1)\ldots x(N-1)\in\mathbb C_0^N\subset \mathbb C^N$ with the normalization condition
$\sum\limits_{k=0}^{N-1} x(k)=0$.
It is proved that the operator
$\Delta:\mathbb C_0^N\to\mathbb C_0^N$ where
$\Delta [x]=y=y(0)y(1)\ldots y(N-1)$,
$y(k)=x(k+1)-x(k)$, is a bijection and
$\Delta[b_n]=b_{n-1}$. Moreover, according to Malozemov's result, the set of the discrete periodic Bernoulli functions is an infinite cyclic group relative to the cyclic convolution
$x*y(s)=\sum\limits_{j=0}^{N-1}x(j)y(s-j)$ with a neutral element
$b_0$, and
$b_n * b_m=b_{n+m}$.
It is proved that either the set of
$N-1$ cyclic shifts
$x^{k\to}(j)=x(j-k)$ of any discrete periodic Bernoulli function or the set
$\{b_m, b_{m+1},\ldots ,b_{m+N-2}\}$ yields a basis of the space
$\mathbb C_0^N$. The generating function
$\sum\limits_{n=0}^{\infty} b_n t^n$ of a sequence of discrete periodic Bernoulli functions is calculated.
Formulas
$\sum\limits_{k=1}^{N-1}\sin^{2m}({\pi k}/{N})$,
$m\in\mathbb Z$, for calculating the sums of even degrees of sinuses at equidistant nodes of a circle are found by means of these functions and the discrete Fourier transform.
It has been established that a cyclic shift by 1 and the multiplication by
$ -N$ transform these functions of positive order into special polynomials
$P_n(k)$, which were introduced by Bespalov and Korobov and have become popular as the Korobov polynomials of the first kind in the form
$K_n(x)=n!P_n(x)$. We have calculated the Korobov numbers
$K_n=-n!\cdot N\cdot b_n(1)$ up to
$K_{13}$ and the Korobov polynomials up to
$K_7(x)$ for any array size (parameter)
$N$.
Keywords:
discrete Fourier transform, cyclic convolution,finite difference, generating function, Korobov numbers and Korobov polynomials.
UDC:
519.113.3
DOI:
10.17223/20710410/43/2