Pentadiagonal Companion Matrices

Abstract

The class of sparse companion matrices was recently characterized in terms of unit Hessenberg matrices. We determine which sparse companion matrices have the lowest bandwidth, that is, we characterize which sparse companion matrices are permutationally similar to a pentadiagonal matrix and describe how to find the permutation involved. In the process, we determine which of the Fiedler companion matrices are permutationally similar to a pentadiagonal matrix. We also describe how to find a Fiedler factorization, up to transpose, given only its corner entries.

Keywords

• companion matrices
• pentadiagonal matrices
• Fiedler companion matrices
• Hessenberg matrices
• algorithms
• zeros of polynomials