Locally optimal knots and tension parameters for exponential splines

Tension can be applied to cubic splines in order to avoid undesired spurious oscillations. This leads to the well-known (exponential) spline in tension. It is crucial but unfortunately difficult to find suitable tension parameters of interpolating splines in tension. Instead of heuristics, we propose a simultaneous knot placing and tension setting algorithm for least-squares splines in tension which includes interpolating splines in tension as a special case. Moreover, the splines presented here are the foundation of exponential surface splines on fairly arbitrary meshes [K.O. Riedel, Two-dimensional splines on fairly arbitrary meshes, ZAMM—Z. Angew. Math. Mech. 85(3) (2005) 176–188].