Existence of Efficient Points in Vector Optimization and Generalized Bishop–Phelps Theorem

In a set without linear structure equipped with a preorder, we give a general existence result for efficient points. In a topological vector space equipped with a partial order induced by a closed convex cone with a bounded base, we prove another kind of existence result for efficient points; this result does not depend on the Zorn lemma. As applications, we study a solution problem in vector optimization and generalize the Bishop–Phelps theorem to a topological vector space setting by showing that the B-support points of any sequentially complete closed subset A of a topological vector space E is dense in A, where B is any bounded convex subset of E.     

On the Mordell–Weil rank of a surface fibration

Abstract

In this article, we give a new upper bound for the Mordell–Weil rank of a surface fibration and we prove an analog result in positive characteristic.     

A Quantitative Version of the Bishop–Phelps Theorem for Operators in Hilbert Spaces

In this paper, with the help of spectral integral, we show a quantitative version of the Bishop-Phelps theorem for operators in complex Hilbert spaces. Precisely, let H be a complex Hilbert space and 0 ε 1/2. Then for every bounded linear operator T : H → H and x0 ∈ H with ||T|| = 1 = ||x0|| such that ||Tx0|| 1 ε, there exist xε∈ H and a bounded linear operator S : H → H with||S|| = 1 = ||xε|| such that ||Sxε|| = 1, ||xε-x0|| ≤ (2ε)1/2 + 4(2ε)1/2, ||S-T|| ≤(2ε)1/2.     

On the coincidence of the factor and Gondran–Minoux rank functions of matrices over a semiring

We consider the rank functions of matrices over semirings, functions that generalize the classical notion of the rank of a matrix over a field. We study semirings over which the factor and Gondran–Minoux ranks of any matrix coincide. It is shown that every semiring satisfying that condition is a subsemiring of a field. We provide an example of an integral domain over which the factor and Gondran–Minoux ranks are different.     

The Bishop–Phelps–Bollobás and approximate hyperplane series properties

We study the Bishop–Phelps–Bollobás property for operators between Banach spaces. Sufficient conditions are given for generalized direct sums of Banach spaces with respect to a uniformly monotone Banach sequence lattice to have the approximate hyperplane series property. This result implies that Bishop–Phelps–Bollobás theorem holds for operators from ${?}_1$ into such direct sums of Banach spaces. We also show that the direct sum of two spaces with the approximate hyperplane series property has such property whenever the norm of the direct sum is absolute.     

Bishop–Phelps–Bollobás property for certain spaces of operators

We characterize the Banach spaces Y   for which certain subspaces of operators from _L1(μ)$L_1(\mu )$ into Y have the Bishop–Phelps–Bollobás property in terms of a geometric property of Y, namely AHSP. This characterization applies to the spaces of compact and weakly compact operators. New examples of Banach spaces Y with AHSP are provided. We also obtain that certain ideals of Asplund operators satisfy the Bishop–Phelps–Bollobás property.     

Γ-flatness and Bishop–Phelps–Bollobás type theorems for operators

The Bishop–Phelps–Bollobás property deals with simultaneous approximation of an operator T and a vector x at which T nearly attains its norm by an operator $T_0$ and a vector $x_0$, respectively, such that $T_0$ attains its norm at $x_0$. In this note we extend the already known results about the Bishop–Phelps–Bollobás property for Asplund operators to a wider class of Banach spaces and to a wider class of operators. Instead of proving a BPB-type theorem for each space separately we isolate two main notions: Γ-flat operators and Banach spaces with ${\mathrm{ACK}}_{\rho }$ structure. In particular, we prove a general BPB-type theorem for Γ-flat operators acting to a space with ${\mathrm{ACK}}_{\rho }$ structure and show that uniform algebras and spaces with the property β have ${\mathrm{ACK}}_{\rho }$ structure. We also study the stability of the ${\mathrm{ACK}}_{\rho }$ structure under some natural Banach space theory operations. As a consequence, we discover many new examples of spaces Y such that the Bishop–Phelps–Bollobás property for Asplund operators is valid for all pairs of the form ($X,Y$).     

On the existence of special solutions of the generalized Davey–Stewartson system

In this note we show that for certain choice of parameters the hyperbolic–elliptic–elliptic generalized Davey–Stewartson system admits time-dependent travelling wave solutions of the kind given in [V.A. Arkadiev, A.K. Pogrebkov, M.C. Polivanov, Inverse scattering transform method and soliton solutions for Davey–Stewartson II equation, Physica D 36 (1989) 189–197] for the hyperbolic Davey–Stewartson system. These solutions lead to radial solutions as well. We also find the sufficient conditions for non-existence of travelling wave solutions for the hyperbolic–elliptic–elliptic generalized Davey–Stewartson system by using the point of view developed in [A. Eden, T.B. Gürel, E. Kuz, Focusing and defocusing cases of the purely elliptic generalized Davey–Stewartson system, IMA J. Appl. Math. (in press)].     

On the degree of iterates of automorphisms¶of the affine plane

For a polynomial automorphism f of ?² _ℂ, we set τ = deg f ²)/(deg f). We prove that τ≤ 1 if and only if f is triangularizable. In this situation, we show (by using a deep result from number theory known as the theorem of Skolem–Mahler–Lech) that the sequence (deg f ⁿ ) _{n ∈ℕ} is periodic for large n. In the opposite case, we prove that τ is an integer (τ≥ 2) and that the sequence (deg f ⁿ ) _{n ∈ℕ} is a geometric progression of ratio τ. In particular, if f is any automorphism, we obtain the rationality of the formal series . Received: 1 December 1997     

On the automorphisms of some line congruences in ℙ3

The automorphisms of line congruences in ³ are studied via the analysis of the automorphisms of the associated focal loci. This study is applied to a Veronese surface (i.e. to a congruence of chords of a twisted cubic) and to the rational scrolls in the Grassmannian G(1, 3).     

On a mild generalization of the Schönemann irreducibility criterion

We state a mild generalization of the classical Schönemann irreducibility criterion in ?[x] and provide an elementary proof.     

Bishop–Phelps–Bollobás property for bilinear forms on spaces of continuous functions

It is shown that the Bishop–Phelps–Bollobás theorem holds for bilinear forms on the complex \(C_0(L_1)\times C_0(L_2)\) for arbitrary locally compact topological Hausdorff spaces \(L_1\) and \(L_2\).     

Tropical patterns of matrices and the Gondran–Minoux rank function

We introduce the notion of the tropical matrix pattern, which provides a powerful tool to investigate tropical matrices. The above approach is then illustrated by the application to the study of the properties of the Gondran–Minoux rank function. Our main result states that up to a multiplication of matrix rows by non-zero constants the Gondran–Minoux independence of the matrix rows and that of the rows of its tropical pattern are equivalent.We also present a number of applications of our main result. In particular, we show that the problem of checking whether the Gondran–Minoux rank of a matrix is less than a given positive integer can be solved in a polynomial time in the size of the matrix. Another consequence of our main result states that the tropical rank, $\mathit{trop}(A)$, and the determinantal rank, $d(A)$, of tropical matrices satisfy the following inequalities: $\mathit{trop}(A)?\sqrt{\mathit{GMr}(A)}$, $d(A)?\sqrt{\mathit{GMr}(A)}$, $\mathit{trop}(A)?\frac{d(A)+2}{3}$. As an important corollary of this result we obtain that if one of these functions is bounded then the other two are also bounded unlike the situation with the factor and Kapranov ranks.     

Soliton,rational and special solutions of the Korteweg–de Vries hierarchy

Soliton, rational and special solutions for any member of the Korteweg–de Vries hierarchy are presented. It is shown that the soliton solutions are found by means of the Hirota formulae with change of the dispersion relation, special solutions for the Korteweg–de Vries hierarchy are expressed via the transcendents of the first and the second Painlevé hierarchies and rational solutions of members for the Korteveg–de Vries hierarchy can be presented using the Yablonski–Vorobév polynomials.     

Conjugacy classes of affine automorphisms of and linear automorphisms of ℙ n in the Cremona groups

We describe the conjugacy classes of affine automorphisms in the group Aut(n,) (respectively Bir()) of automorphisms (respectively of birational maps) of . From this we deduce also the classification of conjugacy classes of automorphisms of ℙⁿ in the Cremona group Bir().