44 research outputs found
Infeasible Deterministic, Stochastic, and Variance-Reduction Algorithms for Optimization under Orthogonality Constraints
Orthogonality constraints naturally appear in many machine learning problems,
from Principal Components Analysis to robust neural network training. They are
usually solved using Riemannian optimization algorithms, which minimize the
objective function while enforcing the constraint. However, enforcing the
orthogonality constraint can be the most time-consuming operation in such
algorithms. Recently, Ablin & Peyr\'e (2022) proposed the Landing algorithm, a
method with cheap iterations that does not enforce the orthogonality constraint
but is attracted towards the manifold in a smooth manner. In this article, we
provide new practical and theoretical developments for the landing algorithm.
First, the method is extended to the Stiefel manifold, the set of rectangular
orthogonal matrices. We also consider stochastic and variance reduction
algorithms when the cost function is an average of many functions. We
demonstrate that all these methods have the same rate of convergence as their
Riemannian counterparts that exactly enforce the constraint. Finally, our
experiments demonstrate the promise of our approach to an array of
machine-learning problems that involve orthogonality constraints
A Riemannian Proximal Newton Method
In recent years, the proximal gradient method and its variants have been
generalized to Riemannian manifolds for solving optimization problems with an
additively separable structure, i.e., , where is continuously
differentiable, and may be nonsmooth but convex with computationally
reasonable proximal mapping. In this paper, we generalize the proximal Newton
method to embedded submanifolds for solving the type of problem with . The generalization relies on the Weingarten and semismooth
analysis. It is shown that the Riemannian proximal Newton method has a local
superlinear convergence rate under certain reasonable assumptions. Moreover, a
hybrid version is given by concatenating a Riemannian proximal gradient method
and the Riemannian proximal Newton method. It is shown that if the objective
function satisfies the Riemannian KL property and the switch parameter is
chosen appropriately, then the hybrid method converges globally and also has a
local superlinear convergence rate. Numerical experiments on random and
synthetic data are used to demonstrate the performance of the proposed methods
Direct Exoplanet Detection Using L1 Norm Low-Rank Approximation
We propose to use low-rank matrix approximation using the component-wise
L1-norm for direct imaging of exoplanets. Exoplanet detection by direct imaging
is a challenging task for three main reasons: (1) the host star is several
orders of magnitude brighter than exoplanets, (2) the angular distance between
exoplanets and star is usually very small, and (3) the images are affected by
the noises called speckles that are very similar to the exoplanet signal both
in shape and intensity. We first empirically examine the statistical noise
assumptions of the L1 and L2 models, and then we evaluate the performance of
the proposed L1 low-rank approximation (L1-LRA) algorithm based on visual
comparisons and receiver operating characteristic (ROC) curves. We compare the
results of the L1-LRA with the widely used truncated singular value
decomposition (SVD) based on the L2 norm in two different annuli, one close to
the star and one far away.Comment: 13 pages, 4 figures, BNAIC/BeNeLearn 202
Multispectral snapshot demosaicing via non-convex matrix completion
Snapshot mosaic multispectral imagery acquires an undersampled data cube by
acquiring a single spectral measurement per spatial pixel. Sensors which
acquire frequencies, therefore, suffer from severe undersampling of
the full data cube. We show that the missing entries can be accurately imputed
using non-convex techniques from sparse approximation and matrix completion
initialised with traditional demosaicing algorithms. In particular, we observe
the peak signal-to-noise ratio can typically be improved by 2 to 5 dB over
current state-of-the-art methods when simulating a mosaic sensor
measuring both high and low altitude urban and rural scenes as well as
ground-based scenes.Comment: 5 pages, 2 figures, 1 tabl
The (1+1)-dimensional Massive sine-Gordon Field Theory and the Gaussian Wave-functional Approach
The ground, one- and two-particle states of the (1+1)-dimensional massive
sine-Gordon field theory are investigated within the framework of the Gaussian
wave-functional approach. We demonstrate that for a certain region of the
model-parameter space, the vacuum of the field system is asymmetrical.
Furthermore, it is shown that two-particle bound state can exist upon the
asymmetric vacuum for a part of the aforementioned region. Besides, for the
bosonic equivalent to the massive Schwinger model, the masses of the one boson
and two-boson bound states agree with the recent second-order results of a
fermion-mass perturbation calculation when the fermion mass is small.Comment: Latex, 11 pages, 8 figures (EPS files
Mitochondrial dysfunction and biogenesis: do ICU patients die from mitochondrial failure?
Mitochondrial functions include production of energy, activation of programmed cell death, and a number of cell specific tasks, e.g., cell signaling, control of Ca2+ metabolism, and synthesis of a number of important biomolecules. As proper mitochondrial function is critical for normal performance and survival of cells, mitochondrial dysfunction often leads to pathological conditions resulting in various human diseases. Recently mitochondrial dysfunction has been linked to multiple organ failure (MOF) often leading to the death of critical care patients. However, there are two main reasons why this insight did not generate an adequate resonance in clinical settings. First, most data regarding mitochondrial dysfunction in organs susceptible to failure in critical care diseases (liver, kidney, heart, lung, intestine, brain) were collected using animal models. Second, there is no clear therapeutic strategy how acquired mitochondrial dysfunction can be improved. Only the benefit of such therapies will confirm the critical role of mitochondrial dysfunction in clinical settings. Here we summarized data on mitochondrial dysfunction obtained in diverse experimental systems, which are related to conditions seen in intensive care unit (ICU) patients. Particular attention is given to mechanisms that cause cell death and organ dysfunction and to prospective therapeutic strategies, directed to recover mitochondrial function. Collectively the data discussed in this review suggest that appropriate diagnosis and specific treatment of mitochondrial dysfunction in ICU patients may significantly improve the clinical outcome
An Alternating Minimization Algorithm with Trajectory for Direct Exoplanet Detection
Effective image post-processing algorithms are vital for the successful direct imaging of exoplanets. Existing algorithms use techniques based on a low-rank approximation to separate the rotating planet signal from the quasi-static speckles. In this paper, we present a novel approach that iteratively finds the planetâs flux and the low-rank approximation of quasi-static signals, strengthening the existing model based on lowrank approximations. We implement the algorithm with two different norms and test it on data, showing improvement over classical low-rank approaches. Our results highlight the benefits of iterative refinement of low-rank approximation to enhance planet detection