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de Boor evaluation uses quadratic work in the degree
Statement
For a supplied nonempty knot span and degree , a successful call to the loop in de Boor coefficient evaluation on a specified knot span performs exactly coefficient updates when and none when . A call that returns a range failure performs no more than this many updates. Each update uses at most a constant number of scalar arithmetic operations, so the arithmetic work is and the coefficient storage is ; the caller's span search is excluded.
Facts & Assumptions
Given: The finite degree- loop and one already identified nonempty knot span.
de Boor coefficient evaluation on a specified knot span runs, for each , one update for each and retains only local coefficients.
A supplied span index is used; finding the index is not charged to the coefficient evaluation.
Proof
At loop level , there are values of . Therefore a completed loop performs updates; for the loop is empty. A range failure stops the loop early, so every call performs at most this many updates.
Each full update computes a fixed number of subtractions, one division, two multiplications and one addition, independent of ; an exact-zero numerator branch or a range failure can only reduce that count. Initializing and returning the local list takes at most a constant times copies. Thus the scalar arithmetic count is bounded by a constant times , while the list contains at most entries. The excluded span search cannot change either bound.
Depends on
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
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Sources
- Carl de Boor, A Practical Guide to Splines, revised edition, Chapter X, pp. 123–126 (standard reference, not scraped)