The possible shapes of numerical ranges

The possible shapes of numerical ranges

Which convex subsets of C are the numerical range W (A) of some matrix A? This paper gives a precise characterization of these sets. In addition to this we show that for any A there exists a symmetric B of the same size such that W (A) = W (B) thereby settling an open question from [2]. Mathematics Subject Classification (2000). Primary 47A12.

Higher numerical ranges of matrix polynomials

 Let $P(lambda)$ be an $n$-square complex matrix polynomial, and $1 leq k leq n$ be a positive integer. In this paper, some algebraic and geometrical properties of the $k$-numerical range of $P(lambda)$ are investigated. In particular, the relationship between the $k$-numerical range of $P(lambda)$ and the $k$-numerical range of its companion linearization is stated. Moreover, the $k$-numerical...

Generalized numerical ranges of matrix polynomials

In this paper, we introduce the notions of C-numerical range and C-spectrum of matrix polynomials. Some algebraic and geometrical properties are investigated. We also study the relationship between the C-numerical range of a matrix polynomial and the joint C-numerical range of its coefficients.

Shapes and computer generation of numerical ranges of Krein space operators

Corners of multidimensional numerical ranges

The n-dimensional numerical range of a densely defined linear operator T on a complex Hilbert space H is the set of vectors in Cn of the form (〈Te1, e1〉, . . . , 〈Ten, en〉), where e1, . . . , en is an orthonormal system in H, consisting of vectors from the domain of T . We prove that the components of every corner point of the n-dimensional numerical range are eigenvalues of T .