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Add 拟阵 #4850
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赞同!建议与线性规划合并成组合优化,放在数学部分中。还有名称最好用单数 matroid,不用用复数形式。 推荐几篇文章: |
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@Great-designer 看看贵校课件 |
本校课件不能随便看,只放一个局部以证实确实是这样写的。如若不信,恕本人无法提供更多证据。 |
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working on this 拟阵这个概念在组合数学和图论中比较重要,个人认为有必要介绍一下 |
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页面英文名
matroids
我希望能添加的内容是
许多贪心算法以拟阵(Matroids)为理论基础。另外,并非所有的贪心算法都以拟阵为基础。
对于线性无关,有性质:
一个线性无关向量组的任意子集也线性无关。
如果X和Y是两个线性无关向量组,且X的秩小于Y的秩,则必存在一个y∈Y,使得X∪{y}是一个线性无关向量组。
1935年,美国数学家哈斯勒·惠特尼(Hassler Whitney)把以上两条性质进行了抽象推广,提出了拟阵概念。
一个拟阵是一个满足如下性质的有序对M = (S, I),其中S是非空有限集:
遗传性质:I是S的子集的一个非空族,且若B∈I,且A⊆B,则A∈I。
交换性质:若A∈I, B∈I且|A| < |B|,则存在某个元素x∈B – A,使得A∪{x}∈I。
拟阵有许多案例,例如“矩阵拟阵”和“图拟阵”等等。
线性无关向量组的矩阵构成矩阵拟阵中的I。
森林构成图拟阵中的I。
S的子集的非空族,若满足遗传性质,称为S的独立子集。
给定加权拟阵M = (S, I),计算S的具有最大权值w(A)的独立子集 A∈I ,称为拟阵M的最优子集。
对于具有正权函数的加权拟阵,贪心算法可以返回一个最优子集。
基于拟阵的贪心算法有很多,例如最小生成树的Kruskal算法,以及单位时间任务调度问题的算法。
Prim算法也是贪心算法的例子,但是不满足拟阵的遗传性质,故不属于基于拟阵的贪心算法。
我了解到的相关参考资料有
可以添加到“杂项”。
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