## 2008.55: Deflating Quadratic Matrix Polynomials

2008.55:
Christopher J. Munro
(2007)
*Deflating Quadratic Matrix Polynomials.*
Masters thesis, The University of Manchester.

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## Abstract

In this thesis we consider algorithms for solving the quadratic eigenvalue problem, (lambda^2*A_2 + lambda*A_1 + A_0)x=0 when the leading or trailing coefficient matrices are singular. In a finite element discretization this corresponds to the mass or stiffness matrices being singular and reflects modes of vibration (or eigenvalues) at zero or ``infinity''. We are interested in deflation procedures that enable us to utilize knowledge of the presence of these (or any) eigenvalues to reduce the overall cost in computing the remaining eigenvalues and eigenvectors of interest. We first give an introduction to the quadratic eigenvalue problem and explain how it can be solved by a process called linearization.

We present two types of algorithms, firstly a modification of an algorithm published by Kublanovskaya, Mikhailov, and Khazanov in the 1970s that has recently been translated into English. Using these ideas we present algorithms that are able to reduce the size of the problem by ``deflating'' infinite and zero eigenvalues that arise when the mass or stiffness matrix (or both) are singular.

Secondly we look at methods that deflate zero and infinite eigenvalues by the use of Householder reflectors; this requires a basis for the null space of the mass or stiffness matrix (or both), so we also summarize various decompositions that can be used to give this information. We consider different applications that yield a quadratic eigenvalue problem with singular leading and trailing coefficients and after testing the implementations of the algorithms on some of these problems we comment on their stability.

Item Type: | Thesis (Masters) |
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Uncontrolled Keywords: | quadratic eigenvalue problem, deflation, singular matrix coefficient, matrix polynomial, companion linearization |

Subjects: | MSC 2000 > 15 Linear and multilinear algebra; matrix theory MSC 2000 > 65 Numerical analysis |

MIMS number: | 2008.55 |

Deposited By: | Chris Munro |

Deposited On: | 07 May 2008 |

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