## Abstract

We study an operator c which maps every n-by-n matrix A_{n} to a circulant matrix c(A_{n}) that minimizes the Frobenius norm {norm of matrix}A_{n} - C_{n}{norm of matrix}F over all n-by-n circulant matrices C_{n}. The circulant matrix c(A_{n}), called the optimal circulant preconditioner, has proved to be a good preconditioner for a general class of Toeplitz systems. In this paper, we give different formulations of the operator, discuss its algebraic and geometric properties, and compute its operator norms in different Banach algebras of matrices. Using these results, we are able to give an efficient algorithm for finding the superoptimal circulant preconditioner which is defined to be the minimizer of {norm of matrix}I - C_{n}^{-1}A_{n}{norm of matrix}_{F} over all nonsingular circulant matrices C_{n}.

Original language | English |
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Pages (from-to) | 41-53 |

Number of pages | 13 |

Journal | Linear Algebra and Its Applications |

Volume | 149 |

DOIs | |

Publication status | Published - 15 Apr 1991 |

Externally published | Yes |