Splines and unsorted knot sequences ?
The definition of a B-spline is extended to unordered knot sequences. The resulting smooth piecewise polynomial of minimal support is named U-spline. U-splines can be negative and locally linearly dependent. Yet, linear combinations of U-splines share many B-spline properties including smoothness, polynomial reproduction, and evaluation by recurrence.
spline unsorted knot sequence recurrence de boor basic interval