On normal forms for the similarity classes of matrices and pairs of matrices.

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Bibliographic Details
Title: On normal forms for the similarity classes of matrices and pairs of matrices.
Authors: Bongartz, Klaus1 (AUTHOR) klausbongartz@online.de
Source: Linear Algebra & its Applications. Aug2026, Vol. 743, p76-86. 11p.
Subjects: Normal forms (Mathematics), Linear operators
Abstract: We answer two questions of Kontsevich posed 1998 in the book 'Arnold's problems'. First, over any field k there is a representative system for the similarity classes of n × n -matrices which is a finite disjoint union of affine subspaces. And second, for n ≥ 2 an analogous statement fails for pairs of n × n -matrices over any algebraically closed field of characteristic 0. The positive answer rests on a slight modification of the rational normal form whereas the negative answer requires more work. [ABSTRACT FROM AUTHOR]
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Description
Abstract:We answer two questions of Kontsevich posed 1998 in the book 'Arnold's problems'. First, over any field k there is a representative system for the similarity classes of n × n -matrices which is a finite disjoint union of affine subspaces. And second, for n ≥ 2 an analogous statement fails for pairs of n × n -matrices over any algebraically closed field of characteristic 0. The positive answer rests on a slight modification of the rational normal form whereas the negative answer requires more work. [ABSTRACT FROM AUTHOR]
ISSN:00243795
DOI:10.1016/j.laa.2026.04.017