论文标题

数字计算机上的伪verseverse

Non-Computability of the Pseudoinverse on Digital Computers

论文作者

Boche, Holger, Fono, Adalbert, Kutyniok, Gitta

论文摘要

矩阵的伪源是逆的广义概念,在线性代数中至关重要。但是,没有伪字符的封闭形式表示,可以直接计算出来。因此,必须进行算法计算。只能通过考虑基础硬件(通常是数字硬件)来评估算法计算,该硬件负责逐步执行实际的计算。在本文中,我们分析了伪源是否以及在何种程度上可以在建模为图灵机器的数字硬件平台上计算。为此,我们利用了一个有效算法的概念,该算法描述了一个可证明的正确计算:在输入任何错误参数时,该算法在相对于未知解决方案的给定误差中提供了一个近似值。我们证明,用于计算任何矩阵的伪字词的有效算法在图灵机上都不存在,尽管对于特定的矩阵类别确实存在正确的正确算法。更重要的是,我们的结果在计算图灵机上计算伪源时可以通过算法获得的准确性引入了下限。

The pseudoinverse of a matrix, a generalized notion of the inverse, is of fundamental importance in linear algebra. However, there does not exist a closed form representation of the pseudoinverse, which can be straightforwardly computed. Therefore, an algorithmic computation is necessary. An algorithmic computation can only be evaluated by also considering the underlying hardware, typically digital hardware, which is responsible for performing the actual computations step by step. In this paper, we analyze if and to what degree the pseudoinverse actually can be computed on digital hardware platforms modeled as Turing machines. For this, we utilize the notion of an effective algorithm which describes a provably correct computation: upon an input of any error parameter, the algorithm provides an approximation within the given error bound with respect to the unknown solution. We prove that an effective algorithm for computing the pseudoinverse of any matrix can not exist on a Turing machine, although provably correct algorithms do exist for specific classes of matrices. Even more, our results introduce a lower bound on the accuracy that can be obtained algorithmically when computing the pseudoinverse on Turing machines.

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