Radially symmetric thin plate splines interpolating a circular contour map

Profiles of radially symmetric thin plate spline surfaces minimizing the Beppo Levi energy over a compact annulus $R_1\le r\le R_2$ have been studied by Rabut via reproducing kernel methods. Motivated by our recent construction of Beppo Levi polyspline surfaces, we focus here on minimizing the radial energy over the full semi-axis $0<r<\mathrm{\infty }$. Using a $L$-spline approach, we find two types of minimizing profiles: one is the limit of Rabut’s solution as $R_1\to 0$ and $R_2\to \mathrm{\infty }$ (identified as a `non-singular’ $L$-spline), the other has a second-derivative singularity and matches an extra data value at $0$. For both profiles and $p\in [2,\mathrm{\infty }]$, we establish the $L^p$-approximation order $3\mathrm{/}2+1\mathrm{/}p$ in the radial energy space. We also include numerical examples and obtain a novel representation of the minimizers in terms of dilates of a basis function.