2265636
Polygonal Intersection Searching
30538700
Computing a Ham-Sandwich Cut in Two Dimensions
Let B be a set of n"b black points and W a set of n"w, white points in the Euclidean plane. A line h is said to bisect B (or W) if, at most, half of the points of B (or W) lie on any one side of h. A line that bisects both B and W is called a ham-sandwich cut of B and W. We give an algorithm that computes a ham-sandwich cut of B and W in 0((n"h+n"w) log (min {n"b, n"w}+ 1)) time. The algorithm is considerably simpler than the previous most efficient one which takes 0((n"b + n"w) log (n"b + n"w)) time.
16373684
Counting triangle crossings and halving planes
Every collection of t ≥ 2n<supscrpt>2</supscrpt> triangles witha total of n vertices in <inline-equation><f><blkbd>R</blkbd><sup>3</sup></f></inline-equation> has <inline-equation><f><g>W</g><fen lp="par"><fr><nu>t<sup>4</sup></nu><de>n<sup>6</sup></de></fr><rp post="par"></fen></f></inline-equation> crossing pairs. This implies that one of their edgesmeets<inline-equation><f><g>W</g><fen lp="par"><fr><nu>t<sup>3</sup></nu><de>n<sup>6</sup></de></fr><rp post="par"></fen></f><?Pub Caret></inline-equation> of the triangles. From this it followsthat n points in <inline-equation><f><blkbd>R</blkbd><sup>3</sup></f></inline-equation> have only O(n<supscrpt>8/3</supscrpt>) halvingplanes.
10864618
Stability of persistence diagrams
The persistence diagram of a real-valued function on a topological space is a multiset of points in the extended plane. We prove that under mild assumptions on the function, the persistence diagram is stable: small changes in the function imply only small changes in the diagram. We apply this result to estimating the homology of sets in a metric space and to comparing and classifying geometric shapes.
44420378
Triangulating Topological Spaces
Given a subspace ${\Bbb X} \subseteq {\Bbb R}^d$ and a finite set S⊆ℝd, we introduce the Delaunay complex, ${\cal D}_{\Bbb X}$, restricted by ${\Bbb X}$. Its simplices are spanned by subsets T⊆S for which the common intersection of Voronoi cells meets ${\Bbb X}$ in a non-empty set. By the nerve theorem, $\bigcup {\cal D}_{\Bbb X}$ and ${\Bbb X}$ are homotopy equivalent if all such sets are contractible. This paper proves a sufficient condition for $\bigcup {\cal D}_{\Bbb X}$ and ${\Bbb X}$ be homeomorphic.
30416185
On the Zone Theorem for Hyperplane Arrangements
The zone theorem for an arrangement of n hyperplanes in d-dimensional real space says that the total number of faces bounding the cells intersected by another hyperplane is $O(n^{d - 1} )$. This result is the basis of a time-optimal incremental algorithm that constructs a hyperplane arrangement and has a host of other algorithmic and combinatorial applications. Unfortunately, the original proof of the zone theorem, for $d \geqslant 3$, turned out to contain a serious and irreparable error. This paper presents a new proof of the theorem. The proof is based on an inductive argument, which also applies in the case of pseudohyperplane arrangements. The fallacies of the old proof along with some ways of partially saving that approach are briefly discussed.
6301471
Adaptive Simplicial Grids from Cross-Sections of Monotone Complexes
We study the maintenance of a simplicial grid or complex under changing density requirements. The proposed method works in any fixed dimension and generates grids by projecting cross-sections of a monotone simplicial complex that lives in one dimension higher than the grid. The density of the grid is adapted by locally moving the cross-section up or down along the extra dimension.