Para-Hermitian Rational Matrices

Dopico, FroilΓ‘n M.;Noferini, Vanni;Quintana, MarΓ­a C.;Van Dooren, Paul
(2024) SIAM Journal on Matrix Analysis and Applications β€” Vol. 45, nΒ° 4, p. 2339-2359 (2024)

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  • Dopico, FroilΓ‘n M.orcid-logoUniversidad Carlos III de Madrid, ROR: https://ror.org/03ths8210, Departamento de MatemΓ‘ticas, Avenida de la Universidad, 30 (edificio Sabatini), 28911 LeganΓ©s (Madrid), Spain.
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  • Noferini, Vanniorcid-logoDepartment of Mathematics and Systems Analysis, Aalto University, FI-00076, Finland.
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  • Quintana, MarΓ­a C.orcid-logoDepartment of Mathematics and Systems Analysis, Aalto University, FI-00076, Finland.
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  • Van Dooren, Paulorcid-logoDepartment of Mathematical Engineering, UniversitΓ© catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium.
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Abstract
In this paper, we study para-Hermitian rational matrices and the associated structured rational eigenvalue problem (REP). Para-Hermitian rational matrices are square rational matrices that are Hermitian for all 𝑧 on the unit circle that are not poles. REPs are often solved via linearization, that is, using matrix pencils associated to the corresponding rational matrix that preserve the spectral structure. Yet, nonconstant polynomial matrices cannot be para-Hermitian. Therefore, given a para-Hermitian rational matrix 𝑅⁑(𝑧), we instead construct a βˆ—-palindromic linearization for (1 +𝑧)⁒𝑅⁑(𝑧), whose eigenvalues that are not on the unit circle preserve the symmetries of the zeros and poles of 𝑅⁑(𝑧). This task is achieved via MΓΆbius transformations. We also give a constructive method that is based on an additive decomposition into the stable and antistable parts of 𝑅⁑(𝑧). Analogous results are presented for para-skew-Hermitian rational matrices, i.e., rational matrices that are skew-Hermitian upon evaluation on those points of the unit circle that are not poles.
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Dopico, F. M., Noferini, V., Quintana, M. C., & Van Dooren, P. (2024). Para-Hermitian Rational Matrices. SIAM Journal on Matrix Analysis and Applications, 45(4), 2339-2359. https://doi.org/10.1137/24M1678416 (Original work published 2024)