25,882 research outputs found
Moment-Matching Polynomials
We give a new framework for proving the existence of low-degree, polynomial
approximators for Boolean functions with respect to broad classes of
non-product distributions. Our proofs use techniques related to the classical
moment problem and deviate significantly from known Fourier-based methods,
which require the underlying distribution to have some product structure.
Our main application is the first polynomial-time algorithm for agnostically
learning any function of a constant number of halfspaces with respect to any
log-concave distribution (for any constant accuracy parameter). This result was
not known even for the case of learning the intersection of two halfspaces
without noise. Additionally, we show that in the "smoothed-analysis" setting,
the above results hold with respect to distributions that have sub-exponential
tails, a property satisfied by many natural and well-studied distributions in
machine learning.
Given that our algorithms can be implemented using Support Vector Machines
(SVMs) with a polynomial kernel, these results give a rigorous theoretical
explanation as to why many kernel methods work so well in practice
The combinatorics of associated Hermite polynomials
We develop a combinatorial model of the associated Hermite polynomials and
their moments, and prove their orthogonality with a sign-reversing involution.
We find combinatorial interpretations of the moments as complete matchings,
connected complete matchings, oscillating tableaux, and rooted maps and show
weight-preserving bijections between these objects. Several identities,
linearization formulas, the moment generating function, and a second
combinatorial model are also derived.Comment: [v1]: 18 pages, 16 figures; presented at FPSAC 2007 [v2]: Some minor
errors fixed (thanks Bill Chen, Jang Soo Kim) and text rearranged and cleaned
up; no real content changes [v3]: fixed typos, to appear in European J.
Combinatoric
Higher order matching polynomials and d-orthogonality
We show combinatorially that the higher-order matching polynomials of several
families of graphs are d-orthogonal polynomials. The matching polynomial of a
graph is a generating function for coverings of a graph by disjoint edges; the
higher-order matching polynomial corresponds to coverings by paths. Several
families of classical orthogonal polynomials -- the Chebyshev, Hermite, and
Laguerre polynomials -- can be interpreted as matching polynomials of paths,
cycles, complete graphs, and complete bipartite graphs. The notion of
d-orthogonality is a generalization of the usual idea of orthogonality for
polynomials and we use sign-reversing involutions to show that the higher-order
Chebyshev (first and second kinds), Hermite, and Laguerre polynomials are
d-orthogonal. We also investigate the moments and find generating functions of
those polynomials.Comment: 21 pages, many TikZ figures; v2: minor clarifications and addition
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