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In the field of mathematics known as functional analysis, the invariant subspace problem is a partially unresolved problem asking whether every bounded operator on a complex Banach space sends some non-trivial closed subspace to itself. Many variants of the problem have been solved, by restricting the class of bounded operators considered or by specifying a particular class of Banach spaces. The problem is still open for separable Hilbert spaces (in other words, each example, found so far, of an operator with no non-trivial invariant subspaces is an operator that acts on a Banach space that is not isomorphic to a separable Hilbert space).

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  • Problem invarianter Unterräume (de)
  • Invariant subspace problem (en)
  • 不变子空间问题 (zh)
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  • Das Problem invarianter Unterräume ist eine mathematische Problemstellung aus der Funktionalanalysis. Die Fragestellung lautet, ob jeder nicht-triviale beschränkte und lineare Operator auf einem Banach-Raum einen invarianten Unterraum besitzt. Ein erstes Gegenbeispiel wurde 1975 von dem schwedischen Mathematiker Per Enflo gefunden. Für Hilbert-Räume ist das Problem nach wie vor offen. (de)
  • In the field of mathematics known as functional analysis, the invariant subspace problem is a partially unresolved problem asking whether every bounded operator on a complex Banach space sends some non-trivial closed subspace to itself. Many variants of the problem have been solved, by restricting the class of bounded operators considered or by specifying a particular class of Banach spaces. The problem is still open for separable Hilbert spaces (in other words, each example, found so far, of an operator with no non-trivial invariant subspaces is an operator that acts on a Banach space that is not isomorphic to a separable Hilbert space). (en)
  • 数学领域泛函分析中,最著名的悬而未决的问题之一就是不变子空间问题,有时被乐观地称为不变子空间猜想。这个问题就是如下命题是否成立: 给定一个复希尔伯特空间H,其维度>1,以及一个有界线性算子T : H → H,则H有一个非平凡闭T-不变子空间,也即存在一个H的闭线性子空间W,而且它不同于{0}和H,且使得T(W) ⊆ W。 该命题对于所有2维以上有限维复向量空间是成立的:一个线性算子(矩阵)的特征值是其特征多项式的零点;根据代数基本定理,这个多项式存在零点;一个对应的特征向量可以张成一个不变子空间。该命题也很容易成立如果W不必是闭的:取任意H中非零向量x并考虑H的由{T n(x) : n ≥ 0}线性张成的子空间W. 虽然该猜想的一般情况未获证明,但已经可以列出命题成立的一些特殊情况: * 在希尔伯特空间H可分的情况下该猜想相对比较容易证明(也即,如果它又一个不可数正交基。 * 谱定理表明所有有不变子空间。 * 每个紧算子有不变子空间,由Aronszajn和Smith于1954年证明。紧算子理论在很多方面和有限维空间算子理论相类似,所以该结果并不令人惊讶。 * 波恩斯坦和洛宾逊于1966年证明若T n对于某个正整数n是紧致的,则T有不变子空间。 * V. I. 罗门诺所夫(Lomonosov)于1973年证明若T和某个非零紧算子可交换,则T有不变子空间。 (zh)
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  • Charles Read (en)
  • Per Enflo (en)
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  • Charles (en)
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  • Read (en)
  • Enflo (en)
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