Regularity of irregular subdivision (Q1299987)

The paper is concerned with the irregular case of a univariate subdivision scheme; here not only the original samples are nonequally spaced, but also the new grid points introduced by the subdivision scheme need not to be in the middle between the old ones. The aim of the paper is to study the regularity of limit functions of such irregular subdivision. It is shown that the commutation formula still holds in the irregular case. For the generalization of the four-point scheme introduced by \textit{S. Dubuc} [J. Math. Anal. Appl. 114, 185-204, (1986; Zbl 0615.65005)] and by \textit{N. Dyn, J. A. Gregory} and \textit{D. Levin} [Constructive Approximation 7, No. 2, 127-147 (1991; Zbl 0724.41011)], the authors show that under mild geometric restrictions the limit function is always \(C^1\), and under slightly stronger restrictions, the limit function is even almost \(C^2\).