Paper detail

A construction of linear bounded interpolatory operators on the torus

Let $q\ge 1$ be an integer. Given $M$ samples of a smooth function of $q$ variables, $2π$--periodic in each variable, we consider the problem of constructing a $q$--variate trigonometric polynomial of spherical degree $Ø(M^{1/q})$ which interpolates the given data, remains bounded (independent of $M$) on $[-π,π]^q$, and converges to the function at an optimal rate on the set where the data becomes dense. We prove that the solution of an appropriate optimization problem leads to such an interpolant. Numerical examples are given to demonstrate that this procedure overcomes the Runge phenomenon when interpolation at equidistant nodes on $[-1,1]$ is constructed, and also provides a respectable approximation for bivariate grid data, which does not become dense on the whole domain.