On the value distribution theory of elliptic functions

The Nevanlinna characteristic of a nonconstant elliptic function φ (z) satisfiesT(r, φ)=Kr ² (1+o(1)) asr→∞ whereK is a nonzero constant. In this paper, we completely answer the following question: For which polynomialsQ(z, u ₀,...,u _n ) inu ₀,...,u _n , having coefficientsa(z) satisfyingT(r, a)=o(r ²) asr→∞, will the meromorphic functionh _Q (z)=Q(z, ?(z),...,?⁽ⁿ⁾(z)) either be identically zero or satisfyN(r, 1/h _Q )=o(r ²) asr→∞? In fact, we answer this question for rational functionsQ(z, u ₀,...,u _n ) inu ₀,...,u _n , and also obtain analogous results for the Weierstrass functions ζ(z) and σ(z).     

Idempotent Totally Symmetric Operations on Finite Posets

An n-ary operation f is totally symmetric if it obeys the identity f(x ₁,...,x _n )=f(y ₁,...,y _n ) for all sets of variables such that {x ₁,...,x _n }={y ₁,...,y _n }. We characterize finite posets admitting an n-ary idempotent totally symmetric operation for all n. The characterization is expressed in terms of zigzags, special objects related to the poset. Some open problems concerning idempotent Malcev conditions for order primal algebras are mentioned.     

Abschätzungen der unvollständigen Beta-Funktion in mehreren reellen Variablen und Parametern

The integral ofu ₁ ^p–1 ...u _n ^pn–1 (1–u₁–...–u_n)^q, extended over then-simplex {(u ₁,...,u _n) ₊ ⁿ :u ₁/x ₁+...+u _n/x _n<1}, is estimated from below under the condition thatp ₁+...+p_n+qc=p₁/x₁+...+p_n/x_n=const.     

Elementary operators with H∞-symbols

Let T be a c.n.u. contraction on a Hilbert spaceH and let u-(u₁,...,u_n) be an n-tuple of H(T). We calculate various joint spectra of u(T) and apply the results to study the spectral and index theories of elementary operators associated with n-tuples of the above type.Both authors have been partially supported by NSF grants.     

Functions of elementary random variables and their application to system reliability

Summary LetX ₁,...,X _n be elementary random variables, i.e. random variables taking only finitely many values in . Then for an arbitray functionf(X ₁,...,X _n ) inX ₁,...,X _n a unique polynomial representation with the aid of Lagrange polynomials is given. This easily yields the moments as well as the distribution off(X ₁,...,X _n ) by terms of finitely many moments of the variablesX ₁,...,X _n . For n=1 a necessary and sufficient condition results thatm numbers are the firstm moments of a random variable takingm+1 different values. As an application of random functionsf(X ₁,...,X _n ) the reliability of technical systems with three states is treated.

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Zusammenfassung X ₁, ...,X _n seien elementare Zufallsvariable, d. h., Zufallsvariable, die nur endlich viele reelle Werte annehmen. Mit Hilfe von Lagrangepolynomen wird für eine beliebige Funktionf(X₁,...,X _n ) eine eindeutige polynomiale Darstellung angegeben. Daraus ergeben sich leicht die Momente wie auch die Verteilung von f(X₁,...,X _n ), ausgedrückt durch die Momente der VariablenX ₁,...,X _n . Fürn=1 erhält man eine notwendige und hinreichende Bedingung, daßm Zahlen die erstenm Momente einer Zufallsvariablen sind, diem+1 verschiedene Werte annimmt. Als Anwendung wird die Zuverlässigkeit eines technischen Systems mit drei Zuständen behandelt.

     

On a Liouville-type theorem for linear and nonlinear elliptic differential equations on a torus

We study solutionsu of quasilinear elliptic equations—div(F _p (x,∇u))=0 on ℝ ⁿ , whereF(x,p) is periodic inx=(x ₁,...,x _n ) and satisfies suitable convexity and growth assumptions with respect top. Ifu has asymptotically linear growth, we show thatu is, in fact, a linear function up to a periodic perturbation. This partially generalizes recent results of Avallaneda-Lin from the linear to the nonlinear case, and we also achieve a simplified proof of their results. Our work is motivated by the study of minimals of variational problems on a torus and, moreover, has contact with homogenization theory.     

Modular <Emphasis Type="Italic">W</Emphasis> and <Emphasis Type="Italic">H</Emphasis> Type Lie Algebras

The modular Witt algebra W(p, n) and H(p, 2n) are defined on the polynomial rings Z_p[x₁,...,x_n] and Z_p[X₁,...,x_n, y₁,...,y_n] respectively. We generalize Z_p[x₁,...,xn] and Zp[x₁,...,xn, y₁,...,y_n], so we get the generalized W-type and H-type modular Lie algebras. We find all the derivations of W(p, 1).AMS Subject Classification: Primary 17B40, 17B56.     

Three characterizations of non-binary correlation-immune and resilient functions

A functionf(X ₁,X ₂, ...,X _n ) is said to betth-order correlation-immune if the random variableZ=f(X ₁,X ₂,...,X _n ) is independent of every set oft random variables chosen from the independent equiprobable random variablesX ₁,X ₂,...,X _n . Additionally, if all possible outputs are equally likely, thenf is called at-resilient function. In this paper, we provide three different characterizations oft th-order correlation immune functions and resilient functions where the random variable is overGF (q). The first is in terms of the structure of a certain associated matrix. The second characterization involves Fourier transforms. The third characterization establishes the equivalence of resilient functions and large sets of orthogonal arrays.     

Exchangeable and partially exchangeable random partitions

Summary Call a random partition of the positive integerspartially exchangeable if for each finite sequence of positive integersn ₁,...,n _k, the probability that the partition breaks the firstn ₁+...+n_k integers intok particular classes, of sizesn ₁,...,n_k in order of their first elements, has the same valuep(n ₁,...,n_k) for every possible choice of classes subject to the sizes constraint. A random partition is exchangeable iff it is partially exchangeable for a symmetric functionp(n ₁,...n_k). A representation is given for partially exchangeable random partitions which provides a useful variation of Kingman's representation in the exchangeable case. Results are illustrated by the two-parameter generalization of Ewens' partition structure.Research supported by N.S.F. Grants MCS91-07531 and DMS-9404345     

A note on a strong uniqueness theorem of strauss

In this paper we present a correction of the proof of a strong uniqueness theorem given by H. Strauss^[1] in 1992 on approximation by reciprocals of functions of an n-dimensional space (u₁, … u_n) satisfying coefficient constraints.     

Vector bundles on a product of real cubic curves

In this paper we give a characterization of then-tuples (C ₁,...,C _n ) of nonsingular projective real cubic curves such that every topological complex vector bundle onC ₁×...×C _n admits an algebraic structure. The results are very explicit and can be expressed in an especially simple form for cubies defined over the rationals.The second author was supported by an NSF grant.     

Geometry of the motion of robot manipulators

A p-parametric robot is a mapping g of R^p into the homogeneous space P=C₆×C₆/Diag(C₆×C₆) given by the formula g(u₁,...,u_p=exp u₁X₁..... exp u_pX_p, where C₆, is the Lie group of all congruences of E₃ and X₁,..., X_p are fixed vectors from the Lie algebra of C₆. We characterize the set g(R^p) locally by a system of PDE and give some geometrical properties of g as a p-dimensional motion for p<6. We also characterize the Frenet frame of g and show how to construct it for the robot manipulator given by its axes X₁,...,X_p.     

A note on a strong uniqueness theorem of strauss

In this paper we present a correction of the proof of a strong uniqueness theorem given by H. Strauss^[1] in 1992 on approximation by reciprocals of functions of an n-dimensional space span (u₁, …, u_n) satisfying coefficient constraints.     

Über komplementäre Ungleichungen mit drei Mittelwerten. Teil 1

Earlier investigations are extended to inequalities with three means of the formf(M _? (x;α),M _Ψ (y;α))?M _χ (f(x,y);α)≧0 (I). Replacing the given basic sets (x)=(x ₁,...,x _n ) and (y)=(y ₁,...,y _n ) by two suitably chosen sets (u)=(u ₁,...,u _m ) and (v)=(v ₁,...,v _m ), lower or upper bounds on the left side of (I) can be obtained. In the case of upper bounds these inequalities are complementary to (I). In general, the numberm is not less than 4; it may be reduced under additional hypotheses. Some examples (inequalities complementary to some additive inequalities) are given.     

Constrained Lp-Approximation by Generalized n-Convex Functions Induced by ECT-Systems

The problem of finding a best L_p-approximation (1 ≤ p < ∞) to a function in L_p from a special subcone of generalized n-convex functions induced by an ECT-system is considered. Tchebycheff splines with a countably infinite number of knots are introduced and best approximations are characterized in terms of local best approximations by these splines. Various properties of best approximations and their uniqueness in L₁ are investigated. Some special results for generalized monotone and convex cases are obtained.     

Inequalities for sums of independent geometrical random variables

Summary We give a survey of known results regarding Schur-convexity of probability distribution functions. Then we prove that the functionF(p ₁,...,p_n;t)=P(X₁+...+X_n≤t) is Schur-concave with respect to (p ₁,...,p_n) for every realt, whereX _i are independent geometric random variables with parametersp _i. A generalization to negative binomial random variables is also presented.     

Local invariance principles and their application to density estimation

Summary Letx ₁,...,x _n be independent random variables with uniform distribution over [0, 1] ^d , andX( ⁿ ) be the centered and normalized empirical process associated tox ₁,...,x _n . Given a Vapnik-Chervonenkis classL of bounded functions from [0, 1] ^d intoR of bounded variation, we apply the one-dimensional dyadic scheme of Komlós, Major and Tusnády to get the best possible rate in Dudley's uniform central limit theorem for the empirical process {E ⁽ⁿ⁾(h):hL}. WhenL fulfills some extra condition, we prove there exists some sequenceB _n of Brownian bridges indexed byL such that whereK (L) denotes the maximal variation of the elements ofL. This result is then applied to maximal deviations distributions for kernel density estimators under minimal assumptions on the sequence of bandwith parameters. We also derive some results concerning strong approximations for empirical processes indexed by classes of sets with uniformly small perimeter. For example, it follows from Beck's paper that the above result is optimal, up to a possible factor , whenL is the class of Euclidean balls with radius less thanr.     

Characterization of generalized convex functions by their best approximation in sign-monotone norms

Let {u₀, u₁,… u_{n − 1}} and {u₀, u₁,…, u_n} be Tchebycheff-systems of continuous functions on [a, b] and let f ε C[a, b] be generalized convex with respect to {u₀, u₁,…, u_{n − 1}}. In a series of papers ([1], [2], [3]) D. Amir and Z. Ziegler discuss some properties of elements of best approximation to f from the linear spans of {u₀, u₁,…, u_{n − 1}} and {u₀, u₁,…, u_n} in the L_p-norms, 1 p ∞, and show (under different conditions for different values of p) that these properties, when valid for all subintervals of [a, b], can characterize generalized convex functions. Their methods of proof rely on characterizations of elements of best approximation in the L_p-norms, specific for each value of p. This work extends the above results to approximation in a wider class of norms, called “sign-monotone,” [6], which can be defined by the property: ¦ f(x)¦ ¦ g(x)¦,f(x)g(x) 0, a x b, imply f g . For sign-monotone norms in general, there is neither uniqueness of an element of best approximation, nor theorems characterizing it. Nevertheless, it is possible to derive many common properties of best approximants to generalized convex functions in these norms, by means of the necessary condition proved in [6]. For {u₀, u₁,…, u_n} an Extended-Complete Tchebycheff-system and f ε C⁽ⁿ⁾[a, b] it is shown that the validity of any of these properties on all subintervals of [a, b], implies that f is generalized convex. In the special case of f monotone with respect to a positive function u₀(x), a converse theorem is proved under less restrictive assumptions.     

Über komplementäre Ungleichungen mit drei Mittelwerten. Teil 2

In Part 1 we obtained lower and upper bounds of the expressionf(M _φ(x;α),M _ψ(y;α))?M _χ(f(x,y);α) by replacing the given sets(x)=(x ₁,...,x _n ),(y)=(y ₁,...,y _n ) by two suitably chosen sets ((u)=(u ₁,...,u _m ),(v)=(v ₁,...,v _m ), in general withm≥4. Now, in the case of upper bounds, the numberm will, under additional hypotheses, be reduced tom=3 (§ 4) and finally tom=2 (§ 5). Inequalities, complementary to the inequalities of Hölder and Minkowski and to another inequality are given as illustrations.     

A note on the multiplicity in factor ring

Let (R,m) = k[x ₁,..., x _n ](x ₁,...,x _n ) be a local polynomial ring (k being an algebraically closed field), and Q:= (F ₁,..., F _r )R be a primary ideal in R with respect to a maximal ideal m ⊂ R. In this short note we give a formula for the multiplicity e ₀ (QR/(F ₁)R, R/(F ₁)R). The author was supported by the grant No. 1/0262/03) of the Slovak Ministry of Education.