A unitary Hessenberg QR-based algorithm via semiseparable matrices

  • Authors:
  • Luca Gemignani

  • Affiliations:
  • Dipartimento di Matematica, Unversita' di Pisa, Largo Bruno Pontecorvo 5, 56127, Pisa, Italy

  • Venue:
  • Journal of Computational and Applied Mathematics
  • Year:
  • 2005

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Abstract

In this paper, we present a novel method for solving the unitary Hessenberg eigenvalue problem. In the first phase, an algorithm is designed to transform the unitary matrix into a diagonal-plus-semiseparable form. Then we rely on our earlier adaptation of the QR algorithm to solve the dpss eigenvalue problem in a fast and robust way. Exploiting the structure of the problem enables us to yield a quadratic time using a linear memory space. Nonetheless the algorithm remains robust and converges as fast as the customary QR algorithm. Numerical experiments confirm the effectiveness and the robustness of our approach.