heal.abstract |
In this thesis, we study Krein spaces and their relation to matrix polynomials.
Krein spaces are of very resent origin. This thesis has a lot of references from the
phD of P. Zizler who studied linear operators and matrix polynomials in Krein spaces.
Krein spaces are inner product spaces with an inde nite inner product, which di er
from the known de nite inner product. In the study of in nite dimensional Krein
spaces the basic tool is linear operators. In this thesis, we focus on nite dimensional
Krein spaces, where we use matrix polynomials instead of linear operators. Initially,
in the introductory chapter we present some important properties of the de nite
inner product, the induced norm and of Hilbert spaces. Hilbert spaces are complete
inner product spaces, and there is a close relation of them and Krein spaces. We,
also, introduce the basic elements of matrix polynomials, and we present the Smith
form, from which elementary divisors are arised. Then, in the second chapter, we
de ne the inde nite inner prooduct, and we introduce Krein spaces and Pontryagin
spaces, which are inde nite inner product spaces. In the nite dimensional case, a
Krein space is a Pontryagin space. Consequently, in the third chapter, we study
matrix polynomials and their relation to di erential equations and some important
notions, such as of the sign characteristic and the order of neutrality. Also, there
is a special reference to selfadjoint matrix polynomials. Finally, the fourth chapter
deals with matrix polynomials of constant signature, and the properties of its order
of neutrality. |
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