 # Institute of Mathematics

## On the vectors associated with the roots of max-plus characteristic polynomials

#### Yuki Nishida, Sennosuke Watanabe, Yoshihide Watanabe

###### Received December 28, 2019.   Published online September 15, 2020.

Abstract:  We discuss the eigenvalue problem in the max-plus algebra. For a max-plus square matrix, the roots of its characteristic polynomial are not its eigenvalues. In this paper, we give the notion of algebraic eigenvectors associated with the roots of characteristic polynomials. Algebraic eigenvectors are the analogues of the usual eigenvectors in the following three senses: (1) An algebraic eigenvector satisfies an equation similar to the equation $A\otimes\boldsymbol{x} = \lambda\otimes\boldsymbol{x}$ for usual eigenvectors. Under a suitable assumption, the equation has a nontrivial solution if and only if $\lambda$ is a root of the characteristic polynomial. (2) The set of algebraic eigenvectors forms a max-plus subspace called algebraic eigenspace. (3) The dimension of each algebraic eigenspace is at most the multiplicity of the corresponding root of the characteristic polynomial.
Keywords:  max-plus algebra; eigenvalue; eigenvector; characteristic polynomial
Classification MSC:  15A18, 15A80
DOI:  10.21136/AM.2020.0374-19

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Affiliations:   Yuki Nishida, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan, e-mail: ynishida.cyjc1901@gmail.com; Sennosuke Watanabe, National Institute of Technology, Oyama College, 771 Nakakuki, Oyama, Tochigi 323-0806, Japan, e-mail: sewatana@oyama-ct.ac.jp; Yoshihide Watanabe, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan, e-mail: yowatana@mail.doshisha.ac.jp

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