Stable Liftings of Polynomial Traces on Tetrahedra

Abstract: On the reference tetrahedron $K$, we construct, for each $k \in \mathbb{N}0$, a right inverse for the trace operator $u \mapsto (u, \partial{n} u, \ldots, \partial_{n}^k u)|_{\partial K}$. The operator is stable as a mapping from the trace space of $W^{s, p}(K)$ to $W^{s, p}(K)$ for all $p \in (1, \infty)$ and $s \in (k+1/p, \infty)$. Moreover, if the data is the trace of a polynomial of degree $N \in \mathbb{N}_0$, then the resulting lifting is a polynomial of degree $N$. One consequence of the analysis is a novel characterization for the range of the trace operator.