Algorithm 841: BHESS: Gaussian reduction to a similar banded Hessenberg form

  • Authors:
  • Gary W. Howell;Nadia Diaa

  • Affiliations:
  • North Carolina State University, Raleigh, NC;-

  • Venue:
  • ACM Transactions on Mathematical Software (TOMS)
  • Year:
  • 2005

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Abstract

BHESS uses Gaussian similarity transformations to reduce a general real square matrix to similar upper Hessenberg form. Multipliers are bounded in root mean square by a user-supplied parameter. If the input matrix is not highly nonnormal and the user-supplied tolerance on multipliers is of a size greater than ten, the returned matrix usually has small upper bandwidth. In such a case, eigenvalues of the returned matrix can be determined by the bulge-chasing BR iteration or by Rayleigh quotient iteration. BHESS followed by BR iteration determines a complete spectrum in about one-fifth the time required for orthogonal reduction to Hessenberg form followed by QR iterations. The FORTRAN 77 code provided for BHESS runs efficiently on a cache-based architecture.