运筹学学报

• 运筹学 • 上一篇    下一篇

两伪币的搜索问题

武晓辉1,* 李胜家1   

  1. 1. 山西大学数学科学学院, 太原 030006
  • 收稿日期:2016-05-25 出版日期:2016-12-15 发布日期:2016-12-15
  • 通讯作者: 武晓辉 18734838796@163.com
  • 基金资助:

    基金项目: 国家自然科学基金(No. 61174082)

Searching for two counterfeit coins

WU Xiaohui1,*  LI Shengjia1   

  1. 1. School of Mathematical Sciences, Shanxi University, Taiyuan 030006, China
  • Received:2016-05-25 Online:2016-12-15 Published:2016-12-15

摘要:

考虑两伪币的搜索问题: 给定外观相同的n个硬币, 其中有两个比较重的伪币, 通过等臂天平在尽可能少的称量次数下去找出两个伪币. L^{(2)}(n)为最坏情况下找到两伪币的最小称量步数. 对于任意的 n\geq2, 满足\lceil \log_3\binom{n}{2}\rceil \leq L^{(2)}(n)\leq\lceil \log_3\binom{n}{2}\rceil+1. 猜想信息理论下界均可达. 通过一个新的方法扩大了满足信息理论下界的n的取值范围.

关键词: 组合搜索, 组测试, 称重问题, 两伪币

Abstract:

The following weighting problem is considered: determine two counterfeit coins which are heavier than good coins in a set of n coins of the same appearance using only an equal arms balance. Let L^{(2)}(n) denote the minimum number of weighings necessary when exactly two of n coins are known to be  defective. For all n\geq 2, it satisfies \lceil \log_3\binom{n}{2}\rceil \leq L^{(2)}(n)\leq\lceil \log_3\binom{n}{2}\rceil+1. It was conjectured that the lower bound is always achieved. In this paper, using an novel algorithm, we improve on the range of n for which the lower bound is reached.

Key words: combinatorial search, group testing, weighting problem, two counterfeit coins