529 research outputs found
Holographic-(V)AE: an end-to-end SO(3)-Equivariant (Variational) Autoencoder in Fourier Space
Group-equivariant neural networks have emerged as a data-efficient approach
to solve classification and regression tasks, while respecting the relevant
symmetries of the data. However, little work has been done to extend this
paradigm to the unsupervised and generative domains. Here, we present
Holographic-(V)AE (H-(V)AE), a fully end-to-end SO(3)-equivariant (variational)
autoencoder in Fourier space, suitable for unsupervised learning and generation
of data distributed around a specified origin. H-(V)AE is trained to
reconstruct the spherical Fourier encoding of data, learning in the process a
latent space with a maximally informative invariant embedding alongside an
equivariant frame describing the orientation of the data. We extensively test
the performance of H-(V)AE on diverse datasets and show that its latent space
efficiently encodes the categorical features of spherical images and structural
features of protein atomic environments. Our work can further be seen as a case
study for equivariant modeling of a data distribution by reconstructing its
Fourier encoding
Quantum information processing with noisy cluster states
We provide an analysis of basic quantum information processing protocols
under the effect of intrinsic non-idealities in cluster states. These
non-idealities are based on the introduction of randomness in the entangling
steps that create the cluster state and are motivated by the unavoidable
imperfections faced in creating entanglement using condensed-matter systems.
Aided by the use of an alternative and very efficient method to construct
cluster state configurations, which relies on the concatenation of fundamental
cluster structures, we address quantum state transfer and various fundamental
gate simulations through noisy cluster states. We find that a winning strategy
to limit the effects of noise, is the management of small clusters processed
via just a few measurements. Our study also reinforces recent ideas related to
the optical implementation of a one-way quantum computer.Comment: 13 pages, 13 figures, RevTe
Liouville quantum gravity with matter central charge in : a probabilistic approach
There is a substantial literature concerning Liouville quantum gravity (LQG)
in two dimensions with conformal matter field of central charge
. Via the DDK ansatz, LQG can
equivalently be described as the random geometry obtained by exponentiating
times a variant of the planar Gaussian free field (GFF), where
satisfies .
Physics considerations suggest that LQG should also make sense in the regime
when . However, the behavior in this regime is rather
mysterious in part because the corresponding value of is complex, so
analytic continuations of various formulas give complex answers which are
difficult to interpret in a probabilistic setting.
We introduce and study a discretization of LQG which makes sense for all
values of . Our discretization consists
of a random planar map, defined as the adjacency graph of a tiling of the plane
by dyadic squares which all have approximately the same "LQG size" with respect
to the GFF. We prove that several formulas for dimension-related quantities are
still valid for , with the caveat that the
dimension is infinite when the formulas give a complex answer. In particular,
we prove an extension of the (geometric) KPZ formula for , which gives a finite quantum dimension iff the Euclidean
dimension is at most . We also show that the
graph distance between typical points with respect to our discrete model grows
polynomially whereas the cardinality of a graph distance ball of radius
grows faster than any power of (which suggests that the Hausdorff dimension
of LQG is infinite for ).
We include a substantial list of open problems.Comment: 53 pages, 6 figure
Simple integrative preprocessing preserves what is shared in data sources
<p>Abstract</p> <p>Background</p> <p>Bioinformatics data analysis toolbox needs general-purpose, fast and easily interpretable preprocessing tools that perform data integration during exploratory data analysis. Our focus is on vector-valued data sources, each consisting of measurements of the same entity but on different variables, and on tasks where source-specific variation is considered noisy or not interesting. Principal components analysis of all sources combined together is an obvious choice if it is not important to distinguish between data source-specific and shared variation. Canonical Correlation Analysis (CCA) focuses on mutual dependencies and discards source-specific "noise" but it produces a separate set of components for each source.</p> <p>Results</p> <p>It turns out that components given by CCA can be combined easily to produce a linear and hence fast and easily interpretable feature extraction method. The method fuses together several sources, such that the properties they share are preserved. Source-specific variation is discarded as uninteresting. We give the details and implement them in a software tool. The method is demonstrated on gene expression measurements in three case studies: classification of cell cycle regulated genes in yeast, identification of differentially expressed genes in leukemia, and defining stress response in yeast. The software package is available at <url>http://www.cis.hut.fi/projects/mi/software/drCCA/</url>.</p> <p>Conclusion</p> <p>We introduced a method for the task of data fusion for exploratory data analysis, when statistical dependencies between the sources and not within a source are interesting. The method uses canonical correlation analysis in a new way for dimensionality reduction, and inherits its good properties of being simple, fast, and easily interpretable as a linear projection.</p
Geometric integrator for Langevin systems with quaternion-based rotational degrees of freedom and hydrodynamic interactions
We introduce new Langevin-type equations describing the rotational and translational motion of rigid bodies interacting through conservative and non-conservative forces, and hydrodynamic coupling. In the absence of non-conservative forces the Langevin-type equations sample from the canonical ensemble. The rotational degrees of freedom are described using quaternions, the lengths of which are exactly preserved by the stochastic dynamics. For the proposed Langevin-type equations, we construct a weak 2nd order geometric integrator which preserves the main geometric features of the continuous dynamics. The integrator uses Verlet-type splitting for the deterministic part of Langevin equations appropriately combined with an exactly integrated Ornstein-Uhlenbeck process. Numerical experiments are presented to illustrate both the new Langevin model and the numerical method for it, as well as to demonstrate how inertia and the coupling of rotational and translational motion can introduce qualitatively distinct behaviours
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