TY - JOUR

T1 - Searching for mobile intruders in a polygonal region by a group of mobile searchers

AU - Yamashita, Masafumi

AU - Umemoto, H.

AU - Suzuki, I.

AU - Kameda, T.

PY - 2001/1/1

Y1 - 2001/1/1

N2 - The problem of searching for mobile intruders in a polygonal region by mobile searchers is considered. A searcher can move continuously inside a polygon holding a flashlight that emits a single ray of light whose direction can be changed continuously. The vision of a searcher at any time instant is limited to the points on the ray. The intruders can move continuously with unbounded speed. We denote by ps(P) the polygon search number of a simple polygon P, which is the number of searchers necessary and sufficient to search P. Let n, r, b, and g be the number of edges, the number of reflex vertices, the bushiness, and the size of a minimum guard set of P, respectively. In this paper we present matching upper and (worst case) lower bounds of 1 + [log3(2b + 1)J on ps(P). Also upper bounds on ps(P) in terms of n, r, and g are presented; ps(P) ≤ 1 + Log3(n - 3)J, ps(P) ≤ 1 + [Log3 r], and ps(P) ≤ 2 + [log2 g]. These upper bounds are tight or almost tight in the worst case, since we show that for any natural number s ≥ 2, there is a polygon P such that ps(P) = log3(n + 1) = log3(2r + 3) = 1+ log3(2g - 1) = s.

AB - The problem of searching for mobile intruders in a polygonal region by mobile searchers is considered. A searcher can move continuously inside a polygon holding a flashlight that emits a single ray of light whose direction can be changed continuously. The vision of a searcher at any time instant is limited to the points on the ray. The intruders can move continuously with unbounded speed. We denote by ps(P) the polygon search number of a simple polygon P, which is the number of searchers necessary and sufficient to search P. Let n, r, b, and g be the number of edges, the number of reflex vertices, the bushiness, and the size of a minimum guard set of P, respectively. In this paper we present matching upper and (worst case) lower bounds of 1 + [log3(2b + 1)J on ps(P). Also upper bounds on ps(P) in terms of n, r, and g are presented; ps(P) ≤ 1 + Log3(n - 3)J, ps(P) ≤ 1 + [Log3 r], and ps(P) ≤ 2 + [log2 g]. These upper bounds are tight or almost tight in the worst case, since we show that for any natural number s ≥ 2, there is a polygon P such that ps(P) = log3(n + 1) = log3(2r + 3) = 1+ log3(2g - 1) = s.

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U2 - 10.1007/s00453-001-0045-3

DO - 10.1007/s00453-001-0045-3

M3 - Article

AN - SCOPUS:0242269948

VL - 31

SP - 208

EP - 236

JO - Algorithmica

JF - Algorithmica

SN - 0178-4617

IS - 2

ER -