For any n-by-n complex matrix A and any k, 1 ≤ k ≤ n, let Λk(A) = {λ ∈ C : X∗AX = λIk for some n-by-k X satisfying X∗X = Ik} be its rank-k numerical range. It is shown that if A is an n-by-n contraction, then Λk(A) = ∩{Λk(U) : U is an (n + dA)-by-(n + dA) unitary dilation of A}, where dA = rank (In − A∗A). This extends and refines previous results of Choi and Li on constrained unitary dilations...

To a higher rank directed graph (Λ, d), in the sense of Kumjian and Pask, 2000, one can associate natural noncommutative analytic Toeplitz algebras, both weakly closed and norm closed. We introduce methods for the classification of these algebras in the case of single vertex graphs.

The higher rank numerical range is closely connected to the construction of quantum error correction code for a noisy quantum channel. It is known that if a normal matrix A ∈ Mn has eigenvalues a1, . . . , an, then its higher rank numerical range Λk(A) is the intersection of convex polygons with vertices aj1 , . . . , ajn−k+1 , where 1 ≤ j1 < · · · < jn−k+1 ≤ n. In this paper, it is shown that ...

| Low rank estimators for higher order statistics are considered in this paper. Rank reduction methods ooer a general principle for trading estimator bias for reduced estimator variance. The bias-variance tradeoo is analyzed for low rank estimators of higher order statistics using a tensor product formulation for the moments and cumulants. In general the low rank estimators have a larger bias a...

The problem of relating volume to degree for maps between Riemannian manifolds is a fundamental one. Gromov’s Volume Comparison Theorem [Gr] gives such a relation for maps into negatively curved manifolds. In this paper we extend Gromov’s theorem to locally symmetric manifolds of nonpositive curvature. We derive this as a consequence of the following result, which we believe to be of independen...

Need to do:. • Rewrite the section on triality groups. • Verify that Z ⊂ M q in proof of 6.5. ([PR] says it's true on p. 385.)

We study extensions of higher-rank abelian TNS actions (i.e. hyperbolic and with a special structure of the stable distributions) by compact connected Lie groups. We show that up to a constant, there are only finitely many cohomology classes. We also show the existence of cocycles over higher-rank abelian TNS actions that are not cohomologous to constant cocycles. This is in contrast to earlier...

this paper presents a multi-attribute decision-making model to rank and select the best zones of the city of tehran in order to add new emergency services. the purpose of this decision-making problem is to prioritize the zones having a higher need to emergency services, so that the emergency services to people in different zones get optimized. a multi-criteria decision making model is presented...

We investigate rigidity of measurable structure for higher rank abelian algebraic actions. In particular, we show that ergodic measures for these actions fiber over a 0 entropy measure with Haar measures along the leaves. We deduce various rigidity theorems for isomorphisms and joinings as corollaries.