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On two conjectures concerning convex curves
 Internat. J. Math. vol
"... Abstract. In this paper we recall two basic conjectures on the developables of convex projective curves, prove one of them and disprove the other in the first nontrivial case of curves in RP 3. Namely, we show that i) the tangent developable of any convex curve in RP 3 has degree 4 and ii) construct ..."
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Abstract. In this paper we recall two basic conjectures on the developables of convex projective curves, prove one of them and disprove the other in the first nontrivial case of curves in RP 3. Namely, we show that i) the tangent developable of any convex curve in RP 3 has degree 4 and ii) construct an example of 4 tangent lines to a convex curve in RP 3 such that no real line intersects all four of them. The question (discussed in [EG1] and [So4]) whether the second conjecture is true in the special case of rational normal curves still remains open. We start with some important notions. §1. Introduction and results Main definition. A smooth closed curve γ: S 1 → RP n is called locally convex if the local multiplicity of intersection of γ with any hyperplane H ⊂ RP n at any of the intersection points does not exceed n = dim RP n and globally convex or just convex if the above condition holds for the global multiplicity, i.e for the sum of local multiplicities.
HUATYPE INTEGRALS OVER UNITARY GROUPS AND OVER PROJECTIVE LIMITS OF UNITARY GROUPS
, 2001
"... We discuss some natural maps from a unitary group U(n) to a smaller group U(n−m). (These maps are versions of the Livˇsic characteristic function.) We calculate explicitly the direct images of the Haar measure under some maps. We evaluate some matrix integrals over classical groups and some symmetri ..."
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We discuss some natural maps from a unitary group U(n) to a smaller group U(n−m). (These maps are versions of the Livˇsic characteristic function.) We calculate explicitly the direct images of the Haar measure under some maps. We evaluate some matrix integrals over classical groups and some symmetric spaces. (Values of the integrals are products of Ɣfunctions.) These integrals generalize Hua integrals. We construct inverse limits of unitary groups equipped with analogues of Haar measure and evaluate some integrals over these inverse limits. Let K be the real numbers R, the complex numbers C, or the algebra of quaternions H. By U(n, K) = O(n), U(n), Sp(n), we denote the unitary group of the space K n = R n, C n, H n. We also use the notation U ◦ (n, K): = SO(n), U(n), Sp(n) for the connected component of the group U(n, K). By σn, we denote the Haar measure on U ◦ (n, K) normalized by the condition σn(U ◦ (n, K)) = 1. Let Q be a matrix over K. By [Q]p, we denote the upper left block of the matrix Q of size p × p. By {Q}p, we denote the lower right block of size p × p. Let us represent a matrix g ∈ U ◦ (n, K) as an (m + (n − m)) × (m + (n − m)) block matrix () P Q. Consider the map
A note on Lagrangian loci of quotients
 Canadian Math. Bull
"... Abstract. We study hamiltonian actions of compact groups in the presence of compatible involutions. We show that the lagrangian fixed point set on the symplectically reduced space is isomorphic to the disjoint union of the involutively reduced spaces corresponding to the conjugacy classes of involut ..."
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Cited by 4 (2 self)
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Abstract. We study hamiltonian actions of compact groups in the presence of compatible involutions. We show that the lagrangian fixed point set on the symplectically reduced space is isomorphic to the disjoint union of the involutively reduced spaces corresponding to the conjugacy classes of involutions on the group strongly inner to the given one. Our techniques imply that the solution to the additive Thompson problem for a given real form can be relayed to the quasisplit real form in the same inner class. We also consider invariant quotients with respect to the corresponding real form of the complexified group. 1.
Spectral approach to linear programming bounds on codes, Problems of Information Transmission
, 2006
"... ABSTRACT. We give new proofs of asymptotic upper bounds of coding theory obtained within the frame of Delsarte’s linear programming method. The proofs rely on the analysis of eigenvectors of some finitedimensional operators related to orthogonal polynomials. The examples of the method considered in ..."
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ABSTRACT. We give new proofs of asymptotic upper bounds of coding theory obtained within the frame of Delsarte’s linear programming method. The proofs rely on the analysis of eigenvectors of some finitedimensional operators related to orthogonal polynomials. The examples of the method considered in the paper include binary codes, binary constantweight codes, spherical codes, and codes in the projective spaces. 1. Introduction. Let X be a compact metric space with distance function d. A code C is a finite subset of X. Define the minimum distance of C as d(C) = minx,y∈C,x=y d(x,y). A variety of metric spaces that arise from different applications include the binary Hamming space, the binary Johnson space, the sphere in R n, real and complex projective spaces, Grassmann manifolds, etc. Estimating the maximum size of the code with a given value of d is one of the main problems of coding theory. Let M be the cardinality of
Two Conjectures on Convex Curves
, 2002
"... In this paper we recall two basic conjectures on the developables of convex projective curves, prove one of them and disprove the other in the first nontrivial case of . Namely, we show i) that the tangent developable of any convex curve in has degree 4 and ii) construct an example of 4 tange ..."
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In this paper we recall two basic conjectures on the developables of convex projective curves, prove one of them and disprove the other in the first nontrivial case of . Namely, we show i) that the tangent developable of any convex curve in has degree 4 and ii) construct an example of 4 tangent lines to a convex curve in RP such that no real line intersects all four of them. The question (discussed in [EG1] and [So4]) whether the second conjecture is true in the special case of rational normal curves still remains open.
Foundations Of Temporal Query Languages
, 1995
"... Temporal Databases are repositories of information dependent on time. The major difference from standard, e.g., relational database systems, is the need of storing possibly infinite objects, e.g., time spans. In recent years, there have been numerous proposals that introduce time into standard relat ..."
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Temporal Databases are repositories of information dependent on time. The major difference from standard, e.g., relational database systems, is the need of storing possibly infinite objects, e.g., time spans. In recent years, there have been numerous proposals that introduce time into standard relational systems. Unfortunately, most of the attempts have been based on adhoc extensions of existing database systems and query languages, e.g., TQUEL and TSQL. Such extensions often create many problems, when precise semantics needs to be developed, if one exists at all. In a recent survey by J. Chomicki, a clean way of defining temporal databases based on logic was proposed. This methodology views temporal databases as multisorted, finitely representable firstorder structures. Query languages then became formulas in suitable logics over the vocabulary of such structures. This method has been quite successful, as most of the existing proposals are subsumed by this approach with only minor ...
Efficient Computation of Trellis Code Generating Functions
 IEEE TRANS. COMMUN
, 2004
"... For trellis codes, generating function techniques provide the distance spectrum and a union bound on biterror rate. The computation of the generating function of a trellis code may be separated into two stages. The first stage reduces the number of states as much as possible using lowcomplexity ap ..."
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For trellis codes, generating function techniques provide the distance spectrum and a union bound on biterror rate. The computation of the generating function of a trellis code may be separated into two stages. The first stage reduces the number of states as much as possible using lowcomplexity approaches. The second stage produces the generating function from the reduced state diagram through some form of matrix inversion, which has a relatively high complexity. In this paper, we improve on the amount of state reduction possible during the lowcomplexity first stage. We also show that for a trellis code that is a linear convolutional code followed by a signal mapper, the number of states may always be reduced from to (( ) 2) + 1 using lowcomplexity techniques. Finally, we analytically compare the complexity of various matrix inversion techniques and verify through simulation that the twostage approach we propose has the lowest complexity. In an example, the new technique produced the union bound in about half the time required by the best algorithm already in the literature.
Simultaneous stabilization, avoidance and Goldberg’s constants
, 2011
"... Dedicated to the memory of A. Goldberg and V. Logvinenko This is an exposition for mathematicians of some unsolved problems arising in control theory of linear timeindependent systems. The earliest automatic control devices that I know are described in the book of Hero of Alexandria “Pneumatica”, s ..."
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Dedicated to the memory of A. Goldberg and V. Logvinenko This is an exposition for mathematicians of some unsolved problems arising in control theory of linear timeindependent systems. The earliest automatic control devices that I know are described in the book of Hero of Alexandria “Pneumatica”, see Fig. 1. In the modern times these devices are omnipresent (almost every home appliance contains at least one, a car has several, an airplane or a guided missile has many; an ingenious mechanical steering device of a sailboat permits you to sleep and to dine during your voyage, while it keeps prescribed direction with respect to the wind; one can add many other examples). Mathematical theory of these devices begins, as far as I know, with George Biddell Airy (of the Airy function), Astronomer Royal, who investigated mathematically stabilization of the clockwork mechanism directing his equatorial. 1 The stability condition that “all poles must be in the left halfplane” was explicitly stated for the first time by J. C. Maxwell [18]. Parallel research