12,971 research outputs found
Lifting to the spectral ball with interpolation
We give necessary and sufficient conditions for solving the spectral
Nevanlinna--Pick lifting problem. This reduces the spectral Nevanlinna--Pick
problem to a jet interpolation problem into the symmetrized polydisc.Comment: 7 pages; corrections to references and typo
Stein Spaces Characterized by their Endomorphisms
Finite dimensional Stein spaces admitting a proper holomorphic embedding of
the complex line are characterized, among all complex spaces, by their
holomorphic endomorphism semigroup in the sense that any semigroup isomorphism
induces either a biholomorphic or an antibiholomorphic map between them.Comment: 15 pages; additional references in the introduction; corrected typo
Breakout character of islet amyloid polypeptide hydrophobic mutations at the onset of type-2 diabetes
Toxic fibrillar aggregates of Islet Amyloid PolyPeptide (IAPP) appear as the
physical outcome of a peptidic phase-transition signaling the onset of type-2
diabetes mellitus in different mammalian species. In particular, experimentally
verified mutations on the amyloidogenic segment 20-29 in humans, cats and rats
are highly correlated with the molecular aggregation propensities. Through a
microcanonical analysis of the aggregation of IAPP_{20-29} isoforms, we show
that a minimalist one-bead hydrophobic-polar continuum model for protein
interactions properly quantifies those propensities from free-energy barriers.
Our results highlight the central role of sequence-dependent hydrophobic
mutations on hot spots for stabilization, and so for the engineering, of such
biological peptides.Comment: 8 pages, 6 figures, 1 table; final version to appear in Physical
Review
Nonextensive lattice gauge theories: algorithms and methods
High-energy phenomena presenting strong dynamical correlations, long-range
interactions and microscopic memory effects are well described by nonextensive
versions of the canonical Boltzmann-Gibbs statistical mechanics. After a brief
theoretical review, we introduce a class of generalized heat-bath algorithms
that enable Monte Carlo lattice simulations of gauge fields on the nonextensive
statistical ensemble of Tsallis. The algorithmic performance is evaluated as a
function of the Tsallis parameter q in equilibrium and nonequilibrium setups.
Then, we revisit short-time dynamic techniques, which in contrast to usual
simulations in equilibrium present negligible finite-size effects and no
critical slowing down. As an application, we investigate the short-time
critical behaviour of the nonextensive hot Yang-Mills theory at q- values
obtained from heavy-ion collision experiments. Our results imply that, when the
equivalence of statistical ensembles is obeyed, the long-standing universality
arguments relating gauge theories and spin systems hold also for the
nonextensive framework.Comment: to appear in Comput. Phys. Com
Teaching decision theory proof strategies using a crowdsourcing problem
Teaching how to derive minimax decision rules can be challenging because of
the lack of examples that are simple enough to be used in the classroom.
Motivated by this challenge, we provide a new example that illustrates the use
of standard techniques in the derivation of optimal decision rules under the
Bayes and minimax approaches. We discuss how to predict the value of an unknown
quantity, , given the opinions of experts. An
important example of such crowdsourcing problem occurs in modern cosmology,
where indicates whether a given galaxy is merging or not, and are the opinions from astronomers regarding . We use
the obtained prediction rules to discuss advantages and disadvantages of the
Bayes and minimax approaches to decision theory. The material presented here is
intended to be taught to first-year graduate students.Comment: 21 pages, 2 figures. This is an Accepted Manuscript of an article
published by Taylor & Francis Group in The American Statistician, available
online: https://amstat.tandfonline.com/doi/abs/10.1080/00031305.2016.126431
The fibred density property and the automorphism group of the spectral ball
We generalize the notion of the density property for complex manifolds to
holomorphic fibrations, and introduce the notion of the fibred density
property. We prove that the natural fibration of the spectral ball over the
symmetrized polydisc enjoys the fibred density property and describe the
automorphism group of the spectral ball.Comment: 23 pages; major changes in Section 5 concerning the dimension
estimates of the kernel of homogeneous derivation
A Spectral Series Approach to High-Dimensional Nonparametric Regression
A key question in modern statistics is how to make fast and reliable
inferences for complex, high-dimensional data. While there has been much
interest in sparse techniques, current methods do not generalize well to data
with nonlinear structure. In this work, we present an orthogonal series
estimator for predictors that are complex aggregate objects, such as natural
images, galaxy spectra, trajectories, and movies. Our series approach ties
together ideas from kernel machine learning, and Fourier methods. We expand the
unknown regression on the data in terms of the eigenfunctions of a kernel-based
operator, and we take advantage of orthogonality of the basis with respect to
the underlying data distribution, P, to speed up computations and tuning of
parameters. If the kernel is appropriately chosen, then the eigenfunctions
adapt to the intrinsic geometry and dimension of the data. We provide
theoretical guarantees for a radial kernel with varying bandwidth, and we
relate smoothness of the regression function with respect to P to sparsity in
the eigenbasis. Finally, using simulated and real-world data, we systematically
compare the performance of the spectral series approach with classical kernel
smoothing, k-nearest neighbors regression, kernel ridge regression, and
state-of-the-art manifold and local regression methods
Converting High-Dimensional Regression to High-Dimensional Conditional Density Estimation
There is a growing demand for nonparametric conditional density estimators
(CDEs) in fields such as astronomy and economics. In astronomy, for example,
one can dramatically improve estimates of the parameters that dictate the
evolution of the Universe by working with full conditional densities instead of
regression (i.e., conditional mean) estimates. More generally, standard
regression falls short in any prediction problem where the distribution of the
response is more complex with multi-modality, asymmetry or heteroscedastic
noise. Nevertheless, much of the work on high-dimensional inference concerns
regression and classification only, whereas research on density estimation has
lagged behind. Here we propose FlexCode, a fully nonparametric approach to
conditional density estimation that reformulates CDE as a non-parametric
orthogonal series problem where the expansion coefficients are estimated by
regression. By taking such an approach, one can efficiently estimate
conditional densities and not just expectations in high dimensions by drawing
upon the success in high-dimensional regression. Depending on the choice of
regression procedure, our method can adapt to a variety of challenging
high-dimensional settings with different structures in the data (e.g., a large
number of irrelevant components and nonlinear manifold structure) as well as
different data types (e.g., functional data, mixed data types and sample sets).
We study the theoretical and empirical performance of our proposed method, and
we compare our approach with traditional conditional density estimators on
simulated as well as real-world data, such as photometric galaxy data, Twitter
data, and line-of-sight velocities in a galaxy cluster
Logically-consistent hypothesis testing in the hexagon of oppositions
Although logical consistency is desirable in scientific research, standard
statistical hypothesis tests are typically logically inconsistent. In order to
address this issue, previous work introduced agnostic hypothesis tests and
proved that they can be logically consistent while retaining statistical
optimality properties. This paper characterizes the credal modalities in
agnostic hypothesis tests and uses the hexagon of oppositions to explain the
logical relations between these modalities. Geometric solids that are composed
of hexagons of oppositions illustrate the conditions for these modalities to be
logically consistent. Prisms composed of hexagons of oppositions show how the
credal modalities obtained from two agnostic tests vary according to their
threshold values. Nested hexagons of oppositions summarize logical relations
between the credal modalities in these tests and prove new relations.Comment: 25 pages, 9 figure
Pragmatic hypotheses in the evolution of science
This paper introduces pragmatic hypotheses and relates this concept to the
spiral of scientific evolution. Previous works determined a characterization of
logically consistent statistical hypothesis tests and showed that the modal
operators obtained from this test can be represented in the hexagon of
oppositions. However, despite the importance of precise hypothesis in science,
they cannot be accepted by logically consistent tests. Here, we show that this
dilemma can be overcome by the use of pragmatic versions of precise hypotheses.
These pragmatic versions allow a level of imprecision in the hypothesis that is
small relative to other experimental conditions. The introduction of pragmatic
hypotheses allows the evolution of scientific theories based on statistical
hypothesis testing to be interpreted using the narratological structure of
hexagonal spirals, as defined by Pierre Gallais
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