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Linking the TPR1, DPR1 and arrow-head matrix structures. (English) Zbl 1132.15009
Summary: Some recent polynomial root-finders rely on effective solution of the eigenproblem for special matrices such as DPR1 (that is, diagonal plus rank-one) and arrow-head matrices. We examine the correlation between these two classes and their links to the Frobenius companion matrix, and we show a Gauss similarity transform of a TPR1 (that is, triangular plus rank-one) matrix into DPR1 and arrow-head matrices. Theoretically, the known unitary similarity transforms of a general matrix into a block triangular matrix with TPR1 diagonal blocks enable the extension of the cited effective eigen-solvers from DPR1 and arrow-head matrices to general matrices. Practically, however, the numerical stability problems with these transforms may limit their value to some special classes of input matrices.

##### MSC:
 15A18 Eigenvalues, singular values, and eigenvectors 15B57 Hermitian, skew-Hermitian, and related matrices 65H05 Numerical computation of solutions to single equations 12Y05 Computational aspects of field theory and polynomials (MSC2010) 26C10 Real polynomials: location of zeros 65F15 Numerical computation of eigenvalues and eigenvectors of matrices
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