We study the existence and characterization properties of compact Hermitian operators C on a Hilbert space H such that the norm of C is less or equal to that of C + D , for all the real and compact diagonals D in a fixed ...

We study the C* -algebra D+K which consists of sums of a diagonal plus a compact operator. We describe the structure of the unitary group, the sets of ideals, automorphisms and projections.

We present quasi-diagonal preconditioners for piecewise polynomial discretizations of pseudodifferential operators of order minus two in any space dimension. Here, quasi-diagonal means diagonal up to a sparse transformation. ...

In this note we study the structure of shift-preserving operators acting on a finitely generated shift-invariant space. We define a new notion of diagonalization for these operators, which we call s-diagonalization. We ...

Let H be a separable infinite-dimensional complex Hilbert space, B(H) the algebra of bounded linear operators acting on H and J a proper two-sided ideal of B(H). Denote by UJ(H) the group of all unitary operators of the ...

If X is the set of compact or p-Schatten operators over a complex Hilbert separable space H, we study the existence and characterization properties of Hermitian A∈X such that |||A|||≤|||A+D|||,for allD∈D(X) or equivalently ...

We analyse the interplay between maximal/minimal/adjoint ideals of multilinear operators (between sequence spaces) and their associated Köthe sequence spaces. We establish relationships with spaces of multipliers and apply ...

We present quasi-diagonal preconditioners for piecewise polynomial discretizations of pseudodifferential operators of order minus two in any space dimension. Here, quasi-diagonal means diagonal up to a sparse transformation. ...

We study extendibility of diagonal multilinear operators from Lp to Lq spaces. We determine the values of p and q for which every diagonal n-linear operator is extendible, and those for which the only extendible ones are ...