The Eta Invariant and the Real Connective K-Theory of the Classifying Space for Quaternion Groups

We express the real connective K-theory groups o_4k–1(B Q ) ofthe quaternion group Q of order = 2 ^j 8 in terms of therepresentation theory of Q by showing o_4k–1(B Q ) = Sp(S ^4k+3/Q )where is any fixed point free representation of Q in U(2k + 2).     

A necessary condition for convergence of interpolating parabolic and cubic splines

Let the sequence of nets _n be such that , where h_i ⁽ⁿ⁾ are the lengths of the segments of a net. The bound is necessary in order that interpolating parabolic and cubic splines converge for any function in C ( = 0) or C(0 < < 1), where C is the class of functions satisfying a Lipschitz condition of order. It is also shown that this bound cannot essentially be weakened.Translated from Matematicheskie Zametki, Vol. 19, No. 2, pp. 165–178, February, 1976.The author thanks Yu. N. Subbotin for a useful discussion of the results obtained.     

Bijectivity of -endomorphisms of ℬ(H) and the unilateral shift

LetH be a separable infinite-dimensional complex Hilbert space. We prove that if : (H)(H) is a^*-preserving ring homomorphism whose range contains a rank-one operator and an operator with dense range, then is an isometric linear or conjugate-linear algebra automorphism of (H). In particular, if the unilateral shift is contained in the range of a^*-endomorphism of (H), then is bijective.Research partially supported by the Hungarian National Research Science Foundation, Operating Grant Number OTKA 1652 and K&H Bank Ltd., Universitas Foundation.     

A spectral mapping theorem for scalar-type spectral operators in locally convex spaces

LetT be a continuous scalar-type spectral operator defined on a quasi-complete locally convex spaceX, that is,T=fdP whereP is an equicontinuous spectral measure inX andf is aP-integrable function. It is shown that (T) is precisely the closedP-essential range of the functionf or equivalently, that (T) is equal to the support of the (unique) equicontinuous spectral measureQ ^* defined on the Borel sets of the extended complex plane ^* such thatQ ^*({})=0 andT=zdQ _*(z). This result is then used to prove a spectral mapping theorem; namely, thatg((T))=(g(T)) for anyQ ^*-integrable functiong: ^{* *} which is continuous on (T). This is an improvement on previous results of this type since it covers the case wheng((T))/{} is an unbounded set in a phenomenon which occurs often for continuous operatorsT defined in non-normable spacesX.     

Path properties of kernel generated two-time parameter Gaussian processes

Summary We study path properties of two-parameter Gaussian processes {X(t,v),t R} of the formX(t,v)= _{0 –} (t,v,x,y)dW(x,y), where the kernel function (t, v, x, y) is assumed to be square integrable in (x, y) onR×R ⁺, andW(x, y) is a standard two-parameter Wiener process.Work partially supported by an NSERC Canada Operating Grant at Carleton UniversityWork supported by an NSERC Canada International Scientific Exchange Award at Carleton University and by National Natural Science Foundation of China     

The minimum independence number for designs

Fort=2,3 andk2t–1 we prove the existence oft–(n,k,) designs with independence numberC _,k n ^{(k–t)/(k–1)} (ln n) ^1/(k–1) . This is, up to the constant factor, the best possible.Some other related results are considered.Supported by NSF Grant DMS-9011850     

Large deviations for the invariant measure of a reaction-diffusion equation with non-Gaussian perturbations

Summary In this paper we establish a large deviations principle for the invariant measure of the non-Gaussian stochastic partial differential equation (SPDE) _t v =v +f(x,v )+(x,v ) . Here is a strongly-elliptic second-order operator with constant coefficients, h:=DH _xx-h, and the space variablex takes values on the unit circleS ¹. The functionsf and are of sufficient regularity to ensure existence and uniqueness of a solution of the stochastic PDE, and in particular we require that 0<mM wherem andM are some finite positive constants. The perturbationW is a Brownian sheet. It is well-known that under some simple assumptions, the solutionv ² is aC ^k (S ¹)-valued Markov process for each 0<1/2, whereC (S ¹) is the Banach space of real-valued continuous functions onS ¹ which are Hölder-continuous of exponent . We prove, under some further natural assumptions onf and which imply that the zero element ofC (S ¹) is a globally exponentially stable critical point of the unperturbed equation _t ⁰ = ⁰ +f(x,⁰), that has a unique stationary distributionv ^K, on (C (S ¹), (C ^K (S ¹))) when the perturbation parameter is small enough. Some further calculations show that as tends to zero,v ^K, tends tov ^K,0, the point mass centered on the zero element ofC (S ¹). The main goal of this paper is to show that in factv ^K, is governed by a large deviations principle (LDP). Our starting point in establishing the LDP forv ^K, is the LDP for the process , which has been shown in an earlier paper. Our methods of deriving the LDP forv ^K, based on the LDP for are slightly non-standard compared to the corresponding proofs for finite-dimensional stochastic differential equations, since the state spaceC (S ¹) is inherently infinite-dimensional.This work was performed while the author was with the Department of Mathematics, University of Maryland, College Park, MD 20742, USA     

A new stochastic approximation procedure using quantile curves

Summary Suppose that for each real number x we can sample at will from a population having unknown distribution function F _x (·), that p is a fixed number in (0,1), that a is a fixed real number, and that there is a unique unknown value of x (call it ) such that is the p-th quantile of F .We propose scheme for sequentially approximating , present a theorem giving conditions under which these approximations converge to with probability one, discuss the conditions of the theorem, give some examples, and mention some variations.The research of this author was supported by National Science Foundation Grant No. MCS 77-00841The research of this author was supported by the Research Foundation of the State University of New York     

Groups acting simply transitively on the vertices of a building of typeà 2, II: The casesq=2 andq=3

If (P, L) is a projective plane and is a triangle presentation compatible with a point-line correspondence :P L, then gives rise to a group and a thick building of typeà ₂ on the vertices of which acts simply transitively. We find all triangle presentations (up to natural equivalence) compatible with some point-line correspondence :P L, when (P, L) is the projective plane of orderq=2 orq=3. For some, but not all, of these , is isomorphic to the building associated withG=PGL(3,K) whereK is a local field with discrete valuation and residual field of orderq. We identify the for which this is the case, and in these cases, find embeddings of intoG. We also describe the arithmetic nature of these groups.     

Two new unconstrained optimization algorithms which use function and gradient values

Two new methods for unconstrained optimization are presented. Both methods employ a hybrid direction strategy which is a modification of Powell's 1970 dogleg strategy. They also employ a projection technique introduced by Davidon in his 1975 algorithm which uses projection images of x and g in updating the approximate Hessian. The first method uses Davidon's optimally conditioned update formula, while the second uses only the BFGS update. Both methods performed well without Powell's special iterations and singularity safeguards, and the numerical results are very promising.This research was supported by the National Science Foundation under Grant No. GJ-40903.     

Posets isomorphic to their extensions

A standard extension for a poset P is a system Q of lower ends (descending subsets) of P containing all principal ideals of P. An isomorphism between P and Q is called recycling if [Y]Q for all YQ. The existence of such an isomorphism has rather restrictive consequences for the system Q in question. For example, if Q contains all lower ends generated by chains then a recycling isomorphism between P and Q forces Q to be precisely the system of all principal ideals. For certain standard extensions Q, it turns out that every isomorphism between P and Q (if there is any) must be recycling. Our results include the well-known fact that a poset cannot be isomorphic to the system of all lower ends, as well as the fact that a poset is isomorphic to the system of all ideals (i.e., directed lower ends) only if every ideal is principal.     

The uniform convergence of the sum of independent random variables

LetX _i (i=1, 2, ...) be the independent random variables on the probability space (, ,P). In this paper we will show that the necessary and sufficient condition of the uniform convergence of X _i is the convergence of m _i ⁽¹⁾ and m _i ⁽⁰⁾ , wherem _i ⁽¹⁾ , m _i ⁽⁰⁾ denote the 1-quantile and 0-quantile ofX _i respectively.     

Stability of the method of lines

Summary It is well known that a necessary condition for the Lax-stability of the method of lines is that the eigenvalues of the spatial discretization operator, scaled by the time stepk, lie within a distanceO(k) of the stability region of the time integration formula ask0. In this paper we show that a necessary and sufficient condition for stability, except for an algebraic factor, is that the -pseudo-eigenvalues of the same operator lie within a distanceO()+O(k) of the stability region ask, 0. Our results generalize those of an earlier paper by considering: (a) Runge-Kutta and other one-step formulas, (b) implicit as well as explicit linear multistep formulas, (c) weighted norms, (d) algebraic stability, (e) finite and infinite time intervals, and (f) stability regions with cusps.In summary, the theory presented in this paper amounts to a transplantation of the Kreiss matrix theorem from the unit disk (for simple power iterations) to an arbitrary stability region (for method of lines calculations).Work supported by an NSF Presidential Young Investigator Award to L.N. Trefethen     

The core of a chain complete poset with no one-way infinite fence and no tower

Like dismantling for finite posets, a perfect sequence = P : of a chain complete posetP represents a canonical procedure to produce a coreP . It has been proved that if the posetP contains no infinite antichain then this coreP is a retract ofP andP has the fixed point property iffP has this property. In this paper the condition of having no infinite antichain is replaced by a weaker one. We show that the same conclusion holds under the assumption thatP does not contain a one-way infinite fence or a tower.Supported by a grant from The National Natural Science Foundation of China.     

Random integral representations for classes of limit distributions similar to levy class L 0

Summary For a bounded linear operator Q, on a Banach space E, and a real number , there are introduced classes, U (Q), of some limit distributions such that U _O(I coincides with the Lévy class L ₀. Elements from U (Q are characterized in terms of convolution equations and as probability distributions of some random integral functionals. The continuity and fixed points of this random mapping is studied. It is shown that fixed points coincide with the class of Q-stable measures.This work partially supported by AFOSR Grant No. F49620 82 C 0009     

Non-Arguesian configurations and gluings of modular lattices

In two earlier papers, we investigated non-Arguesian projectivity configurations, d=(d_ij:I,j 5), in a modular latticeL, and the associated intervalsI =u /z , 5. Here we study the relationship of d to representations of L as a gluing of proper intervals. We are primarily concerned with two extreme cases:L=J F withJ an ideal andF a filter; and, whenL is of finite length,L=U {L(x):x S(L)} with S(L), the prime skeleton ofL and eachL(x), a maximal complemented subinterval ofL.Presented by Ralph Freese.Research supported by NSERC Operating Grant A-8190 and the University of Hawaii.Research supported by NSF Grant DMS-8300107.     

Partitioning arrangements of lines I: An efficient deterministic algorithm

In this paper we consider the following problem: Given a set ofn lines in the plane, partition the plane intoO(r ²) triangles so that no triangle meets more thanO(n/r) lines of . We present a deterministic algorithm for this problem withO(nr logn/r) running time, where is a constant <3.33.Work on this paper has been supported by Office of Naval Research Grant N00014-87-K-0129, by National Science Foundation Grant DCR-83-20085, and by grants from the Digital Equipment Corporation and the IBM Corporation. A preliminary version of this paper appears in theProceedings of the 5th Annual Symposium on Computational Geometry, 1989, pp. 11–22.     

On arrangements of Jordan arcs with three intersections per pair

Motivated by a number of motion-planning questions, we investigate in this paper some general topological and combinatorial properties of the boundary of the union ofn regions bounded by Jordan curves in the plane. We show that, under some fairly weak conditions, a simply connected surface can be constructed that exactly covers this union and whose boundary has combinatorial complexity that is nearly linear, even though the covered region can have quadratic complexity. In the case where our regions are delimited by Jordan acrs in the upper halfplane starting and ending on thex-axis such that any pair of arcs intersect in at most three points, we prove that the total number of subarcs that appear on the boundary of the union is only (n(n)), where(n) is the extremely slowly growing functional inverse of Ackermann's function.The first author is pleased to acknowledge the support of Amoco Fnd. Fac. Dev. Comput. Sci. 1-6-44862 and National Science Foundation Grant CCR-8714565. Work on this paper by the fourth and seventh authors has been supported by Office of Naval Research Grant N00014-87-K-0129, by National Science Foundation Grant NSF-DCR-83-20085, and by grants from the Digital Equipment Corporation and the IBM Corporation. The seventh author in addition wishes to acknowledge support by a research grant from the NCRD—the Israeli National Council for Research and Development. The fifth author would like to acknowledge support in part by NSF grant DMS-8501947. Finally, the eighth author was supported in part by a National Science Foundation Graduate Fellowship.     

An infinite-dimensional version of the Borsuk-Ulam theorem

We study the solvability of the equation a(x) = f(x) on a sphere in a Banach space, where a is a closed surjective linear operator and f is an odd a-compact map. We also estimate the topological dimension of the solution set and give applications of the corresponding theorem to some problems in differential equations and other fields of mathematics.Translated from Funktsionalnyi Analiz i Ego Prilozheniya, Vol. 38, No. 4, pp. 1–5, 2004Original Russian Text Copyright © by B. D. GelmanSupported by the Russian Foundation for Basic Research, Grant No. 02-01-00189.     

On the general motion-planning problem with two degrees of freedom

We show that, under reasonable assumptions, any collision-avoiding motion-planning problem for a moving system with two degrees of freedom can be solved in timeO( _s (n) log² n), wheren is the number of collision constraints imposed on the system,s is a fixed parameter depending, e.g., on the maximum algebraic degree of these constraints, and _s (n) is the (almost linear) maximum length of (n, s) Davenport-Schinzel sequences. This follows from an upper bound ofO( _s (n)) that we establish for the combinatorial complexity of a single connected component of the space of all free placements of the moving system. Although our study is motivated by motion planning, it is actually a study of topological, combinatorial, and algorithmic issues involving a single face in an arrangement of curves. Our results thus extend beyond the area of motion planning, and have applications in many other areas.Work on this paper by the second author has been supported by Office of Naval Research Grant N00014-82-K-0381, by National Science Foundation Grant No. NSF-DCR-83-20085, by grants from the Digital Equipment Corporation, and the IBM Corporation. Work by the second and third authors has also been supported by a research grant from the Joint Ramot-Israeli Ministry of Industry Foundation, and by a research grant from the NCRD—the Israeli National Council for Research and Development.