Affiliation:
1. University of Waterloo, Waterloo, Ontario, Canada
Abstract
We study a bichromatic version of the well-known
k-set problem
: given two sets
R
and
B
of points of total size
n
and an integer
k
, how many subsets of the form
(R
∩
h
) ∪ (
B
∖
h
) can have size exactly
k
over all halfspaces
h
? In the dual, the problem is asymptotically equivalent to determining the worst-case combinatorial complexity of the
k-level
in an arrangement of
n halfspaces
.
Disproving an earlier conjecture by Linhart [1993], we present the first nontrivial upper bound for all
k
≪
n
in two dimensions:
O
(
nk
1/3
+
n
5/6−ϵ
k
2/3+2 ϵ
+
k
2
) for any fixed ϵ<0. In three dimensions, we obtain the bound
O
(
nk
3/2
+
n
0.5034
k
2.4932
+
k
3
). Incidentally, this also implies a new upper bound for the original
k
-set problem in four dimensions:
O
(
n
2
k
3/2
+
n
1.5034
k
2.4932
+
n k
3
), which improves the best previous result for all
k
≪
n
0.923
. Extensions to other cases, such as arrangements of disks, are also discussed.
Publisher
Association for Computing Machinery (ACM)
Subject
Mathematics (miscellaneous)
Cited by
2 articles.
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