Two-Isometries on Pontryagin Spaces

A model for a class of cyclic analytic 2-isometries acting on Pontryagin spaces is given, generalizing a Hilbert space version given by S. Richter. Furthermore, an example is constructed showing that, unlike in the Hilbert space case, a cyclic analytic 2-isometry need not have a cyclic vector in the orthogonal complement of its range.      

Pseudo-monotone complementarity problems in Hilbert space

In this paper, some existence results for a nonlinear complementarity problem involving a pseudo-monotone mapping over an arbitrary closed convex cone in a real Hilbert space are established. In particular, some known existence results for a nonlinear complementarity problem in a finite-dimensional Hilbert space are generalized to an infinite-dimensional real Hilbert space. Applications to a class of nonlinear complementarity problems and the study of the post-critical equilibrium state of a thin elastic plate subjected to unilateral conditions are given.This research was partially supported by the National Science Foundation Grant DMS-89-13089, Department of Energy Grant DE-FG03-87-ER-25028, and Office of Naval Research Grant N00014-89-J-1659. The authors would like to express their sincere thanks to Professor S. Schaible, School of Administration, University of California, Riverside, for his helpful suggestions and comments. They also thank the referees for their comments and suggestions that improved this paper substantially.     

Boundary Relations and Generalized Resolvents of Symmetric Operators in Krein Spaces

The classical Krein-Naimark formula establishes a one-to-one correspondence between the generalized resolvents of a closed symmetric operator in a Hilbert space and the class of Nevanlinna families in a parameter space. Recently it was shown by V.A. Derkach, S. Hassi, M.M. Malamud and H.S.V. de Snoo that these parameter families can be interpreted as so-called Weyl families of boundary relations, and a new proof of the Krein-Naimark formula in the Hilbert space setting was given with the help of a coupling method. The main objective of this paper is to adapt the notion of boundary relations and their Weyl families to the Krein space case and to prove some variants of the Krein-Naimark formula in an indefinite setting.      

Realizations of the canonical representation

A characterisation of the maximal abelian subalgebras of the bounded operators on Hilbert space that are normalised by the canonical representation of the Heisenberg group is given. This is used to classify the perfect realizations of the canonical representation. Based in part on the author’s doctoral thesis (University of Chicago), written under the direction of Professor Tim Steger.     

Covariant quantization of null supermembranes in four-dimensional spacetime

Kharkov State University; Kharkov Physicotechnical Institute, Ukrainian SSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 88, No. 3, pp. 358–375, September, 1991.     

The augmented lagrangian method for equality and inequality constraints in hilbert spaces

In this paper we consider an augmented Lagrangian method for the minimization of a nonlinear functional in the presence of an equality constraint whose image space is in a Hilbert space, an inequality constraint whose image space is finite dimensional, and an affine inequality constraint whose image space is in an infinite dimensional Hilbert space. We obtain local convergence of this method without imposing strict complementarity conditions when the equality, as well as the inequality constraint with finite dimensional image space are augmented. To the author's knowledge this result even generalizes the convergence results which are known when all spaces are finite dimensional.This research was supported by the Air Force Office of Scientific Research under Grant AFOSR-84-0398 and AFOSR-85-0303, by the National Aeronautics and Space Administration under Grant NAG-1-517, and by NSF under Grant UINT-8521208.This research was supported in part by the Fonds zur Förderung der wissenschaftichen Forschung under S3206 and P6005 and by AFOSR-84-0398. Part of this work was performed while the author was visiting the Division of Applied Mathematics, Brown University, Providence, RI, USA.     

Embedding weakly compact sets into Hilbert space

We give an example of a weakly compact set in a Banach space, which does not embed topologically as a weakly compact subset of Hilbert space. We also show that a weakly compact set embeds in a super-reflexive space iff it embeds in Hilbert space. This work was done while the authors were visiting Ohio State University. We wish to thank the Department of mathematics at Ohio State University for their kind hospitality. The work of the first author was partially supported by NSF Grant MPS-74-24249. The work of the second author is a part of his Ph.D. Thesis prepared at the University of California at Berkeley.     

Low-frequency asymptotics of the Green's functions of magnets with spontaneously broken symmetry

Physicotechnical Institute, Ukrainian SSR Academy of Sciences, Kharkov; Kharkov State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 89, No. 2, pp. 293–303, November, 1991.     

Preservation of the Range under Perturbations of an Operator

A sufficient condition for the stability of the range of a positive operator in a Hilbert space is given. As a consequence, we get a class of additive perturbations which preserve regularity of the critical point of a positive operator in a Krein space.

     

Rearrangements of series in a Hilbert space

A theorem on rearrangements of numerical series, proved by Agnew, is extended to series in a Hilbert space. A complete proof is given of Orlicz's theorem on unconditionally convergent series in a Hilbert space.Translated from Matematicheskie Zametki, Vol. 12, No. 3, pp. 275–280, September, 1972.     

A Hilbert bundle characterization of Hilbert C*-modules

The category of Hilbert C*-modules over a given C*-algebra is shown to be equivalent to a certain simply described category of Hilbert bundles (i.e., continuous fields of Hilbert spaces) over the space of pure states of the C*-algebra with the zero functional adjoined.

     

The method of alternating projections and the method of subspace corrections in Hilbert space

A new identity is given in this paper for estimating the norm of the product of nonexpansive operators in Hilbert space. This identity can be applied for the design and analysis of the method of alternating projections and the method of subspace corrections. The method of alternating projections is an iterative algorithm for determining the best approximation to any given point in a Hilbert space from the intersection of a finite number of subspaces by alternatively computing the best approximations from the individual subspaces which make up the intersection. The method of subspace corrections is an iterative algorithm for finding the solution of a linear equation in a Hilbert space by approximately solving equations restricted on a number of closed subspaces which make up the entire space. The new identity given in the paper provides a sharpest possible estimate for the rate of convergence of these algorithms. It is also proved in the paper that the method of alternating projections is essentially equivalent to the method of subspace corrections. Some simple examples of multigrid and domain decomposition methods are given to illustrate the application of the new identity.

     

Orthogonally Complemented Subspaces in Banach Spaces

In this paper, we extend the Moreau (Riesz) decomposition theorem from Hilbert spaces to Banach spaces. Criteria for a closed subspace to be (strongly) orthogonally complemented in a Banach space are given. We prove that every closed subspace of a Banach space X with dim X ≥ 3 (dim X ≤ 2) is strongly orthognally complemented if and only if the Banach space X is isometric to a Hilbert space (resp. strictly convex), which is complementary to the well-known result saying that every closed subspace of a Banach space X is topologically complemented if and only if the Banach space X is isomorphic to a Hilbert space.     

Counterexample to a uniqueness theorem for analytic operator functions

It is proved that there exists a bounded holomorphic operator-function z→F(z), ¦z¦<1, with compact values (in a separable Hilbert space) and such that its boundary values F(S), ¦S¦=1 are compact on one (given) arc of the circle and not compact on the other. The corresponding example is constructed with the help of vectorial Hankel operators.     

H-valued generalized functions and orthogonally scattered measures

Hilbert space valued measures of certain kinds are shown to be projections of orthogonally scattered measures. This result is used to give a representation of Hilbert space valued generalized functions in terms of orthogonally scattered measures. Applications are given to the characterization of deterministic Hilbert sequences and generalized stochastic processes.     

On the existence of optimal integration formulas for analytic functions

Summary In this paper we prove the existence of quadrature formulas that are optimal with respect to a Hilbert space of analytic functions solving a problem unsuccessfully attacked so far. Although we allow the formulas to be of type (2) the optimal formulas will be of the form (1).Supported in part by N.S.F. Grant G.P.-28111.Supported in part by Sonderforschungsbereich 72 at Institute for Applied Mathematics, University of Bonn and N.S.F. Grant G.P.-18609.     

Hilbert spaces of Dirichlet series and their multipliers

We consider various Hilbert spaces of Dirichlet series whose norms are given by weighted norms of the Dirichlet coefficients. We describe the multiplier algebras of these spaces. The functions in the multiplier algebra may or may not extend to be analytic on a larger half-plane than the functions in the Hilbert space.

     

Congruences and quasiidentities on unars

We establish conditions under which the fact that all congruences of two unars (universal algebras with one unary operation) are convergent implies the convergence of manifolds and quasimanifolds generated by these unars. Kharkov University, Kharkov. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 6, pp. 852–856, June, 1997.     

Banach空间上的强混合算子

1999年,L．B．Gonzalez 证明了任意无限维可分 Banach 空间上存在拓扑传递的有界线性算子．这个结果肯定地回答了 S．Rolewicz 提出的问题．本文证明了由 L．B．Gonzalez 所给出的算子实际上是强混合的,同时,对加权移位算子的混合性利用权序列进行了刻划并指出任意无限维可分 Hilbert 空间上存在弱混合而非强混合的有界线性算子．