1,372 research outputs found
Discrete-Continuous ADMM for Transductive Inference in Higher-Order MRFs
This paper introduces a novel algorithm for transductive inference in
higher-order MRFs, where the unary energies are parameterized by a variable
classifier. The considered task is posed as a joint optimization problem in the
continuous classifier parameters and the discrete label variables. In contrast
to prior approaches such as convex relaxations, we propose an advantageous
decoupling of the objective function into discrete and continuous subproblems
and a novel, efficient optimization method related to ADMM. This approach
preserves integrality of the discrete label variables and guarantees global
convergence to a critical point. We demonstrate the advantages of our approach
in several experiments including video object segmentation on the DAVIS data
set and interactive image segmentation
RIFLE: Robust Inference from Low Order Marginals
The ubiquity of missing values in real-world datasets poses a challenge for
statistical inference and can prevent similar datasets from being analyzed in
the same study, precluding many existing datasets from being used for new
analyses. While an extensive collection of packages and algorithms have been
developed for data imputation, the overwhelming majority perform poorly if
there are many missing values and low sample size, which are unfortunately
common characteristics in empirical data. Such low-accuracy estimations
adversely affect the performance of downstream statistical models. We develop a
statistical inference framework for predicting the target variable without
imputing missing values. Our framework, RIFLE (Robust InFerence via Low-order
moment Estimations), estimates low-order moments with corresponding confidence
intervals to learn a distributionally robust model. We specialize our framework
to linear regression and normal discriminant analysis, and we provide
convergence and performance guarantees. This framework can also be adapted to
impute missing data. In numerical experiments, we compare RIFLE with
state-of-the-art approaches (including MICE, Amelia, MissForest, KNN-imputer,
MIDA, and Mean Imputer). Our experiments demonstrate that RIFLE outperforms
other benchmark algorithms when the percentage of missing values is high and/or
when the number of data points is relatively small. RIFLE is publicly
available.Comment: 32 pages, 10 figure
Non-convex Optimization for Machine Learning
A vast majority of machine learning algorithms train their models and perform
inference by solving optimization problems. In order to capture the learning
and prediction problems accurately, structural constraints such as sparsity or
low rank are frequently imposed or else the objective itself is designed to be
a non-convex function. This is especially true of algorithms that operate in
high-dimensional spaces or that train non-linear models such as tensor models
and deep networks.
The freedom to express the learning problem as a non-convex optimization
problem gives immense modeling power to the algorithm designer, but often such
problems are NP-hard to solve. A popular workaround to this has been to relax
non-convex problems to convex ones and use traditional methods to solve the
(convex) relaxed optimization problems. However this approach may be lossy and
nevertheless presents significant challenges for large scale optimization.
On the other hand, direct approaches to non-convex optimization have met with
resounding success in several domains and remain the methods of choice for the
practitioner, as they frequently outperform relaxation-based techniques -
popular heuristics include projected gradient descent and alternating
minimization. However, these are often poorly understood in terms of their
convergence and other properties.
This monograph presents a selection of recent advances that bridge a
long-standing gap in our understanding of these heuristics. The monograph will
lead the reader through several widely used non-convex optimization techniques,
as well as applications thereof. The goal of this monograph is to both,
introduce the rich literature in this area, as well as equip the reader with
the tools and techniques needed to analyze these simple procedures for
non-convex problems.Comment: The official publication is available from now publishers via
http://dx.doi.org/10.1561/220000005
- …