منابع مشابه
The Additivity of Crossing Numbers
It has long been conjectured that the crossing numbers of links are additive under the connected sum of links. This is a difficult problem in knot theory and has been open for more than 100 years. In fact, we do not even know that Cr(K1#K2) = Cr(K1) or Cr(K1#K2) = Cr(K2) holds in general, here K1#K2 is the connected sum of K1 and K2 and Cr(K) stands for the crossing number of the link K. The be...
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The crossing number of a graph is the minimum number of edge intersections in a plane drawing of a graph, where each intersection is counted separately. If instead we count the number of pairs of edges that intersect an odd number of times, we obtain the odd crossing number. We show that there is a graph for which these two concepts differ, answering a well-known open question on crossing numbe...
متن کاملCrossing number, pair-crossing number, and expansion
The crossing number crðGÞ of a graph G is the minimum possible number of edge crossings in a drawing of G in the plane, while the pair-crossing number pcrðGÞ is the smallest number of pairs of edges that cross in a drawing of G in the plane. While crðGÞXpcrðGÞ holds trivially, it is not known whether a strict inequality can ever occur (this question was raised by Mohar and Pach and Tóth). We ai...
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In an earlier paper [3], we studied cycles in graphs that intersect all edge-cuts of prescribed sizes. Passing to a more general setting, we examine the existence of T -joins in grafts that intersect all edge-cuts whose size is in a given set A ⊆ {1, 2, 3}. In particular, we characterize all the contractionminimal grafts admitting no T -joins that intersect all edge-cuts of size 1 and 2. We als...
متن کاملMETAHEURISTIC ALGORITHMS FOR MINIMUM CROSSING NUMBER PROBLEM
This paper presents the application of metaheuristic methods to the minimum crossing number problem for the first time. These algorithms including particle swarm optimization, improved ray optimization, colliding bodies optimization and enhanced colliding bodies optimization. For each method, a pseudo code is provided. The crossing number problem is NP-hard and has important applications in eng...
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ژورنال
عنوان ژورنال: European Journal of Combinatorics
سال: 2013
ISSN: 0195-6698
DOI: 10.1016/j.ejc.2013.02.002