It was shown in [2] that if T is a contraction in a Hilbert space with finite defect (‖T‖ ≤ 1, rank(I−T ∗T ) <∞), and its spectrum σ(T ) doesn’t coincide with the closed unit disk D, then the following Linear Resolvent Growth condition ‖(λI − T )−1‖ ≤ C dist(λ, σ(T )) , λ ∈ C\σ(T ), implies that T is similar to a normal operator. The condition rank(I − T ∗T ) < ∞ characterizes how close is T to...

We classify the connected pseudo-Riemannian manifolds of signature (p, q) with q ≥ 5 so that at each point of M the skew-symmetric curvature operator has constant rank 2 and constant Jordan normal form on the set of spacelike 2 planes and so that the skew-symmetric curvature operator is not nilpotent for at least one point of M .

Quantics tensor train (QTT), a new data-sparse format for one– and multi–dimensional vectors, is based on a bit representation of mode indices followed by a separation of variables. A radix-2 reccurence, that lays behind the famous FFT algorithm, can be efficiently applied to vectors in the QTT format. If input and all intermediate vectors of the FFT algorithm have moderate QTT ranks, the resul...

Abstract. For any function f in L∞(D), let Tf denote the corresponding Toeplitz operator the Bergman space A(D). A recent result of D. Luecking shows that if Tf has finite rank then f must be the zero function. Using a refined version of this result, we show that if all except possibly one of the functions f1, . . . , fm are radial and Tf1 · · · Tfm has finite rank, then one of these functions ...

The purpose of this paper is to characterize when a harmonic function with values in the finite rank operators on a Hilbert space is expressible as a harmonic matrix-valued function. We show that harmonic function with values in the rank 1 normal operators is expressible as a harmonic matrix-valued function. We also prove that for any natural number, n, a harmonic function with values in the ra...

Motivated by the search for a logic for polynomial time, we study rank logic (FPR) which extends fixed-point logic with counting (FPC) by operators that determine the rank of matrices over finite fields. While FPR can express most of the known queries that separate FPC from Ptime, nearly nothing was known about the limitations of its expressive power. In our first main result we show that the e...

We consider the problem of finding the spectrum of an operator taking the form of a low-rank (rank one or two) non-normal perturbation of a well-understood operator, motivated by a number of problems of applied interest which take this form. We use the fact that the system is a low-rank perturbation of a solved problem, together with a simple idea of classical differential geometry (the envelop...