34,236 research outputs found
Asymptotic behavior of positively curved steady Ricci Solitons
In this paper, we analyze the asymptotic behavior of -noncollapsed
and positively curved steady Ricci solitons and prove that any -dimensional
-noncollapsed steady K\"ahler-Ricci soliton with non-negative sectional
curvature must be flat.Comment: This is a final version. We added some details in the proofs of
Proposition 4.3 and Corollary 4.
Loss Tomography from Tree Topologies to General Topologies
Loss tomography has received considerable attention in recent years and a
number of estimators based on maximum likelihood (ML) or Bayesian principles
have been proposed. Almost all of the estimators are devoted to the tree
topology despite the general topology is more common in practice. There has
been few likelihood function devoted to the general topology, not to mention
the estimator. To overcome this, two sets of sufficient statistics for the tree
and general topologies, respectively, are proposed in this paper. Using the
statistics, two likelihood functions, one for a topology, are proposed here and
subsequently two likelihood equations for the general topology, one is
link-based and the other is path-based, are obtained. In addition, a dependence
between subtrees in terms of their estimates is identified for the general
topology and a divide-and-conquer strategy is proposed to deal with the
dependence, which divides a general network into two types of independent
trees. Further, two algorithms, one for a type of the independent trees, are
proposed to estimate the loss rates of each type.Comment: will be submitted for publication. arXiv admin note: substantial text
overlap with arXiv:1009.255
Complete non-compact gradient Ricci solitons with nonnegative Ricci curvature
In this paper, we give a delay estimate of scalar curvature for a complete
non-compact expanding (or steady) gradient Ricci soliton with nonnegative Ricci
curvature. As an application, we prove that any complete non-compact expanding
(or steady) gradient K\"{a}hler-Ricci solitons with positively pinched Ricci
curvature should be Ricci flat. The result answers a question in case of
K\"{a}hler-Ricci solitons proposed by Chow, Lu and Ni in a book.Comment: 18 page
Classification of gradient steady Ricci solitons with linear curvature decay
In this paper, we give a description for steady Ricci solitons with a linear
decay of sectional curvature. In particular, we classify all 3-dimensional
steady Ricci solitons and 4-dimensional -noncollpased steady Ricci
solitons with nonnegative sectional curvature under the linear curvature decay
A Variational Approach on Level sets and Linear Convergence of Variable Bregman Proximal Gradient Method for Nonconvex Optimization Problems
We develop a new variational approach on level sets aiming towards
convergence rate analysis of a variable Bregman proximal gradient (VBPG) method
for a broad class of nonsmooth and nonconvex optimization problems. With this
new approach, we are able to extend the concepts of Bregman proximal mapping
and their corresponding Bregman proximal envelops, Bregman proximal gap
function to nonconvex setting. Properties of these mappings and functions are
examined. An aim of this work is to provide a solid foundation on which further
design and analysis of VBPG for more general nonconvex optimization problems
are possible. Another aim is to provide a unified theory on linear convergence
of VBPG with a particular interest towards proximal gradient methods. Centrol
to our analysis for achieving the above goals is an error bound in terms of
level sets and subdifferentials (level-set subdifferential error bound) along
with its links to other level-set error bounds. As a consequence, we have
established a number of positive results. These newly established results not
only enable us to show that any accumulation of the sequence generated by VBPG
is at least a critical point of the limiting subdifferential or even a critical
point of the proximal subdifferential with a fixed Bregman function in each
iteration, but also provide a fresh perspective that allows us to explore
inner-connections among many known sufficient conditions for linear convergence
of various first-order methods. Along the way, we are able to derive a number
of verifiable conditions for level-set error bounds to hold, obtain linear
convergence of VBPG, and derive necessary conditions and sufficient conditions
for linear convergence relative to a level set for nonsmooth and nonconvex
optimization problems
Higher dimensional steady Ricci solitons with linear curvature decay
We prove that any noncompact -noncollapsed steady Ricci soliton with
nonnegative curvature operator must be rotationally symmetric if it has a
linear curvature decay.Comment: We improve the main results in the previous version of paper without
the assumption of positive Ricci curvatur
Steady Ricci solitons with horizontally -pinched Ricci curvature
In this paper, we prove that any -noncollapsed gradient steady Ricci
soliton with nonnegative curvature operator and horizontally -pinched
Ricci curvature must be rotationally symmetric. As an application, we show that
any -noncollapsed gradient steady Ricci soliton with
nonnegative curvature operator must be rotationally symmetric if it admits a
unique equilibrium point and its scalar curvature satisfies
with
.Comment: Corollary 3.11 is adde
A note on compact -solutions of K\"{a}hler-Ricci flow
In this paper, we give a complete classification of -solutions of
K\"{a}haler-Ricci flow on compact complex manifolds. Namely, they must be
quotients of products of irreducible compact Hermitian symmetric manifolds.Comment: 7 page
Using Conditional Generative Adversarial Networks to Generate Ground-Level Views From Overhead Imagery
This paper develops a deep-learning framework to synthesize a ground-level
view of a location given an overhead image. We propose a novel conditional
generative adversarial network (cGAN) in which the trained generator generates
realistic looking and representative ground-level images using overhead imagery
as auxiliary information. The generator is an encoder-decoder network which
allows us to compare low- and high-level features as well as their
concatenation for encoding the overhead imagery. We also demonstrate how our
framework can be used to perform land cover classification by modifying the
trained cGAN to extract features from overhead imagery. This is interesting
because, although we are using this modified cGAN as a feature extractor for
overhead imagery, it incorporates knowledge of how locations look from the
ground.Comment: 5 pages. arXiv admin note: text overlap with arXiv:1806.0512
Fine-Grained Land Use Classification at the City Scale Using Ground-Level Images
We perform fine-grained land use mapping at the city scale using ground-level
images. Mapping land use is considerably more difficult than mapping land cover
and is generally not possible using overhead imagery as it requires close-up
views and seeing inside buildings. We postulate that the growing collections of
georeferenced, ground-level images suggest an alternate approach to this
geographic knowledge discovery problem. We develop a general framework that
uses Flickr images to map 45 different land-use classes for the City of San
Francisco. Individual images are classified using a novel convolutional neural
network containing two streams, one for recognizing objects and another for
recognizing scenes. This network is trained in an end-to-end manner directly on
the labeled training images. We propose several strategies to overcome the
noisiness of our user-generated data including search-based training set
augmentation and online adaptive training. We derive a ground truth map of San
Francisco in order to evaluate our method. We demonstrate the effectiveness of
our approach through geo-visualization and quantitative analysis. Our framework
achieves over 29% recall at the individual land parcel level which represents a
strong baseline for the challenging 45-way land use classification problem
especially given the noisiness of the image data
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