Integral representation of slowly growing equidistant splines

In this paper we consider equidistant polynomial splines S(x) which may grow as O|x|s. We present an integral representation of such splines with a distribution kernel. This representation is related to the Fourier integral of slowly growing functions. The part of the Fourier exponentials herewith play the so called exponential splines by Schoenberg. The integral representation provides a flexible tool for dealing with the growing equidistant splines. First, it allows us to construct a rich library of splines possessing the property that translations of any such spline form a basis of corresponding spline space. It is shown that any such spline is associated with a dual spline whose translations form a biorthogonal basis. As examples we present solutions of the problems of projection of a growing function onto spline spaces and of spline interpolation of a growing function. We construct formulas for approximate evaluation of splines projecting a function onto the spline space and establish therewith exact estimations of the approximation errors.