Discrete Bessel functions and transform

Abstract

We present a straightforward discretization of the Bessel functions $J_n(x)$ to discrete counterparts $B_n^{(N)}(x_m)$, of $N$ integer orders $n$ on $N$ integer points $x_m\equiv m$, that we call discrete Bessel functions. These are built from a Bessel integral generating function, restricting the Fourier transform over the circle to $N$ points. We show that the discrete Bessel functions satisfy several linear and quadratic relations, particularly Graf's product-displacement formulas, that are exact analogues of well-known relations between the continuous functions. It is noteworthy that these discrete Bessel functions approximate very closely the values of the continuous functions in ranges $n+|m|<N$. For fixed $N$, this provides an $N$-point transform between functions of order and of position,$f_n$ and ${\tilde{f}}_m$, which is efficient for the Fourier analysis of finite decaying signals.

11 pages, 3 figures

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