Every Banach ideal of polynomials is compatible with an operator ideal

We show that for each Banach ideal of homogeneous polynomials, there exists a (necessarily unique) Banach operator ideal compatible with it. Analogously, we prove that any ideal of n-homogeneous polynomials belongs to a coherent sequence of ideals of k-homogeneous polynomials.     

Every Banach Space is Reflexive

The title above is wrong, because the strong dual of a Banach space is too strong to assert that the natural correspondence between a space and its bidual is an isomorphism. However, for many applications it suffices to replace the norm on the first dual by the weak*-structure in order to solve the non-reflexiveness problem [1]. But in this way, only the original vector space is recovered by taking the second dual. In this work we introduce a suitable numerical structure on vector spaces such that Banach balls, or more precisely totally convex modules, arise naturally in duality, namely as a category of Eilenberg–Moore algebras. This numerical structure naturally overlies the weak*-topology on the algebraic dual, so the entire Banach space can be reconstructed as a second dual. Moreover, the isomorphism between the original space and its bidual is the unit of an adjunction between the two-dualisation functors. Notice that the weak*-topology is normable only if it lives on a finite dimensional space; in that case the original space is trivial as well, hence reflexive. So the overlying numerical structure should be something more general than a norm or a seminorm and thus approach theory [2, 3] enters the picture.     

Hilbert polynomials and powers of an ideal

Sunto Nel n1. viene definito il complesso generalizzato di Koszul K(A; E; t) di R-moduli associato ad una matrice A sopra un anello R e un R-modulo E. Si studia poi K(A; E; t) nel caso particolare in cui A sia una matrice della forma B(m, s) data nel n.3. Si dimostra infine che, sotto certe condizioni di finitezza, la lunghezza di ogni modulo d'omologia à una funzione polinomiale in m per m grande, e che per ogni m ≥1 la caratteristica di Euler-Poincaré è il prodotto di un coefficiente binomiale per la caratteristica del complesso di Koszul K(B(1, s); E;0).

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Entrata in Redazione il 18 novemb e 1972.     

The polynomial dual of an operator ideal

We prove that the adjoint of a continuous homogeneous polynomial $P$ between Banach spaces belongs to a given operator ideal $\mathcal I$ if and only if $P$ admits a factorization $P = u \circ Q$ where the adjoint of the linear operator $u$ belongs to $\mathcal I$ . Several consequences of this factorization are obtained, for example we characterize the polynomials whose adjoints are absolutely $p$ -summing.     

The ideal envelope of an operator algebra

A left ideal of any -algebra is an example of an operator algebra with a right contractive approximate identity (r.c.a.i.). Conversely, we show here that operator algebras with a r.c.a.i. should be studied in terms of a certain left ideal of a -algebra. We study operator algebras and their multiplier algebras from the perspective of ``Hamana theory' and using the multiplier algebras introduced by the first author.

     

The Betti polynomials of powers of an ideal

For an ideal I in a regular local ring or a graded ideal I in the polynomial ring we study the limiting behavior of as k goes to infinity. By Kodiyalam’s result it is known that β_i(S/I^k) is a polynomial for large k. We call these polynomials the Kodiyalam polynomials and encode the limiting behavior in their generating polynomial. It is shown that the limiting behavior depends only on the coefficients on the Kodiyalam polynomials in the highest possible degree. For these we exhibit lower bounds in special cases and conjecture that the bounds are valid in general. We also show that the Kodiyalam polynomials have weakly descending degrees and identify a situation where the polynomials all have the highest possible degree.     

Every composition operator is (mean) asymptotically Toeplitz

Nazarov and Shapiro recently showed that, while composition operators on the Hardy space H² can only trivially be Toeplitz, or even “Toeplitz plus compact,” it is an interesting problem to determine which of them can be “asymptotically Toeplitz.” I show here that if “asymptotically” is interpreted in, for example, the Cesàro (C,α) sense (α>0), then every composition operator on H² becomes asymptotically Toeplitz.     

Banach Lattices on Which Every Power-Bounded Operator is Mean Ergodic

Given a Banach lattice E that fails to be countably order complete, we construct a positive compact operator A: E E for which T = I - A is power-bounded and not mean ergodic. As a consequence, by using the theorem of R. Zaharopol, we obtain that if every power-bounded operator in a Banach lattice is mean ergodic then the Banach lattice is reflexive.     

Every completely polynomially bounded operator is similar to a contraction

It is proved that a bounded operator on a Hilbert space is similar to a contraction if and only if it is completely polynomially bounded. This gives a partial answer to Problem 6 of Halmos (Bull. Amer. Math. Soc.76 (1970). 877–933). The set of completely bounded maps between C¹-algebras is studied to obtain some structure, representation, and extension theorems for this class of maps. These allow a characterization of the completely bounded representations, on a Hilbert space, of any subalgebra of a C¹-algebra to be obtained. The result in the title follows by applying this characterization to the disk algebra.     

Every conservative double Hausdorff matrix is a kth absolutely summable operator

Let A denote the set of kth absolutely summable double series. In this paper it is shown that every double conservative Hausdorff matrix is a bounded operator on A.     

Banach algebras associated with linear operator pencils

A direct relationship between the theory of pseudoresolvents and the spectral theory of linear operator pencils is established.     

A linearization for operator polynomials with coefficients in certain operator ideals

Summary For an operator polynomial with coefficients in certain Von Neumann-Schatten classes a linearization is constructed. The linearization also belongs to a Von Neumann-Schatten class, and its regularized Fredholm determinant determines the spectral properties of the original polynomial.     

Covering a compact set in a Banach space by an operator range of a Banach space with basis

A Banach space has the approximation property if and only if every compact set in is in the range of a one-to-one bounded linear operator from a space that has a Schauder basis. Characterizations are given for spaces and quotients of spaces in terms of covering compact sets in by operator ranges from spaces. A Banach space is a space if and only if every compact set in is contained in the closed convex symmetric hull of a basic sequence which converges to zero.

     

Common multiples of operator polynomials with analytic coefficients

This paper describes the main properties of analytic common monic left multiples of a system of monic operator polynomials whose coefficients depend analytically on .This paper was written while the first author was a visiting professor of the Vrije Universiteit at Amsterdam     

Differentiation of an operator valued measure in a Banach rigging

Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 40, No. 5, pp. 658–662, 1988.