A Mathematical Foundation for Adaptation, Learning, Discovery, and Invention in Nonlinear Dynamical Systems

Speaker: 

Professor Rui De Figueiredo

Institution: 

UC Irvine

Time: 

Monday, April 13, 2009 - 4:00pm

Location: 

RH 306

The processes of adaptation, learning, discovery, and invention are expected to play an increasingly significant role in emerging large-scale computationally intelligent (CI) systems. . The meanings of adaptation and learning are well-known. By discovery we mean the process of creating a new hypothesis based on sufficient new data that does not fit existing hypotheses; while by invention, the process of creating (synthesizing) new prototypes by interpolation or extrapolation of existing ones.
In this lecture we will present a kernel-based mathematical approach to the modeling and design of the processes of adaptation, learning, discovery and invention in nonlinear dynamical systems. The approach is based on our previous work in which uncertainty is handled by mathematical approximation theory methods, specifically, by best approximation of nonlinear functionals in an appropriate Reproducing Kernel Hilbert Space (RKHS). This formulation leads to optimal nonlinear system models in the form of artificial neural networks (ANNs) in a natural way, that is, without imposing, a-priori, a neural structure on the system being modeled. For this reason, while connecting with the mathematical foundations on which they are based, we will use ANNs as generic representations of the nonlinear dynamical systems under discussion.
Computer simulation results, some using real data, will be presented to establish and illustrate the theoretical developments.

The Overconvergent de Rham-Witt Complex

Speaker: 

Chris Davis

Institution: 

MIT

Time: 

Thursday, April 2, 2009 - 3:00pm

Location: 

RH 306

The aim of the talk is to describe the overconvergent de Rham-Witt complex. It is a subcomplex of the de Rham-Witt complex and it can be used to compute Monsky-Washnitzer cohomology for affine varieties, and rigid cohomology in general. (All our varieties are over a perfect field of characteristic $p$.)

We will begin by reviewing Monsky-Washnitzer cohomology and the de Rham-Witt complex. Next we will define overconvergent Witt vectors and then the overconvergent de Rham-Witt complex. As time permits, we will say something about the proof of the comparison theorem between Monsky-Washnitzer cohomology and overconvergent de Rham-Witt ohomology.

This is joint work with Andreas Langer and Thomas Zink.

Hodge groups of superelliptic jacobians

Speaker: 

Yuri Zarhin

Institution: 

Pennsylvania State University

Time: 

Thursday, May 7, 2009 - 2:00pm

Location: 

RH 306

The Hodge group (aka special Mumford-Tate group) of a complex abelian variety $X$ is a certain linear reductive algebraic group over the rationals that is closely related to the endomorphism ring of $X$. (For example, the Hodge group is commutative if and only if $X$ is an abelian variety of CM-type.) In this talk I discuss" lower bounds" for the center of Hodge groups of superelliptic jacobians. (This is a joint work with Jiangwei Xue.)

Divisibility properties of values of partial zeta functions at non-positive integers

Speaker: 

Barry Smith

Institution: 

UCI

Time: 

Thursday, April 9, 2009 - 3:00pm

Location: 

RH 306

The values of the partial zeta functions for an abelian extension of number fields at non-positive integers are rational numbers with known bounds on their denominators. David Hayes conjectured that when the associated fields satisfy certain algebraic conditions, the bound at s=0 can be sharpened. I will present a counterexample to Hayes's conjecture. I will then propose a new conjecture sharpening the bounds at arbitrary non-positive integers that implies a weaker version of Hayes conjecture at s=0. I will conclude by proving that the new conjecture is a consequence of the Coates-Sinnott conjecture.

Conformal Equivalence of Triangle Meshes

Speaker: 

Professor Ulrich Pinkall

Institution: 

TU Berlin

Time: 

Tuesday, March 10, 2009 - 4:00pm

Location: 

RH 306

We define a notion of conformal equivalence for discrete surfaces (surfaces composed of euclidean triangles). For example, multiplying the lengths of all edges incident with a single vertex by the same factor is considered to be a conformal change of metric. It turns out that finding a conformally equivalent flat metric on a given discrete surface amounts to minimizing a globally convex functional on the space of all metrics. This functional involves the Lobachevski function (known in the context of computing the volume of hyperbolic tetrahedra). This is not an accident, since surprisingly the whole theory is stongly related to hyperbolic geometry. There are important practical applications of our method to Computer Graphics in the context of texture mapping.

Polymer Depinning Transitions with Loop Exponent One

Speaker: 

Professor Ken Alexander

Institution: 

USC

Time: 

Tuesday, April 28, 2009 - 11:00am

Location: 

RH 306

We consider a polymer with configuration modeled by the trajectory of a Markov chain, interacting with a potential of form u+V_n when it visits a particular state 0 at time n, with V_n representing i.i.d. quenched disorder. There is a critical value of u above which the polymer is pinned by the potential. Typically the probability of an excursion of length n for the underlying Markov chain is taken to decay as a power of n (called the loop exponent), perhaps with a slowly varying correction. A particular case not covered in a number of previous studies is that of loop exponent one, which includes simple random walk in two dimensions. We show that in this case, at all temperatures, the critical values of u in the quenched and annealed models are equal, in contrast to all other loop exponents, for which these critical values are known to differ at least at low temperatures. The work is joint with N. Zygouras.

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