The $L_{2}$-approximation order of surface spline interpolation

We show that if the open, bounded domain $\Omega \subset \mathbb{R}^{d}$ has a sufficiently smooth boundary and if the data function $f$ is sufficiently smooth, then the $L_{p}(\Omega )$-norm of the error between $f$ and its surface spline interpolant is $O(\delta ^{\gamma _{p}+1/2})$ ( $1\leq p\leq \infty$), where $\gamma _{p}:=\min \{m,m-d/2+d/p\}$ and $m$ is an integer parameter specifying the surface spline. In case $p=2$, this lower bound on the approximation order agrees with a previously obtained upper bound, and so we conclude that the $L_{2}$-approximation order of surface spline interpolation is $m+1/2$.