3,119 research outputs found
A Survey on Metric Learning for Feature Vectors and Structured Data
The need for appropriate ways to measure the distance or similarity between
data is ubiquitous in machine learning, pattern recognition and data mining,
but handcrafting such good metrics for specific problems is generally
difficult. This has led to the emergence of metric learning, which aims at
automatically learning a metric from data and has attracted a lot of interest
in machine learning and related fields for the past ten years. This survey
paper proposes a systematic review of the metric learning literature,
highlighting the pros and cons of each approach. We pay particular attention to
Mahalanobis distance metric learning, a well-studied and successful framework,
but additionally present a wide range of methods that have recently emerged as
powerful alternatives, including nonlinear metric learning, similarity learning
and local metric learning. Recent trends and extensions, such as
semi-supervised metric learning, metric learning for histogram data and the
derivation of generalization guarantees, are also covered. Finally, this survey
addresses metric learning for structured data, in particular edit distance
learning, and attempts to give an overview of the remaining challenges in
metric learning for the years to come.Comment: Technical report, 59 pages. Changes in v2: fixed typos and improved
presentation. Changes in v3: fixed typos. Changes in v4: fixed typos and new
method
TagBook: A Semantic Video Representation without Supervision for Event Detection
We consider the problem of event detection in video for scenarios where only
few, or even zero examples are available for training. For this challenging
setting, the prevailing solutions in the literature rely on a semantic video
representation obtained from thousands of pre-trained concept detectors.
Different from existing work, we propose a new semantic video representation
that is based on freely available social tagged videos only, without the need
for training any intermediate concept detectors. We introduce a simple
algorithm that propagates tags from a video's nearest neighbors, similar in
spirit to the ones used for image retrieval, but redesign it for video event
detection by including video source set refinement and varying the video tag
assignment. We call our approach TagBook and study its construction,
descriptiveness and detection performance on the TRECVID 2013 and 2014
multimedia event detection datasets and the Columbia Consumer Video dataset.
Despite its simple nature, the proposed TagBook video representation is
remarkably effective for few-example and zero-example event detection, even
outperforming very recent state-of-the-art alternatives building on supervised
representations.Comment: accepted for publication as a regular paper in the IEEE Transactions
on Multimedi
Exploring the mirror TBA
We apply the contour deformation trick to the Thermodynamic Bethe Ansatz
equations for the AdS_5 \times S^5 mirror model, and obtain the integral
equations determining the energy of two-particle excited states dual to N=4 SYM
operators from the sl(2) sector. We show that each state/operator is described
by its own set of TBA equations. Moreover, we provide evidence that for each
state there are infinitely-many critical values of 't Hooft coupling constant
\lambda, and the excited states integral equations have to be modified each
time one crosses one of those. In particular, estimation based on the large L
asymptotic solution gives \lambda \approx 774 for the first critical value
corresponding to the Konishi operator. Our results indicate that the related
calculations and conclusions of Gromov, Kazakov and Vieira should be
interpreted with caution. The phenomenon we discuss might potentially explain
the mismatch between their recent computation of the scaling dimension of the
Konishi operator and the one done by Roiban and Tseytlin by using the string
theory sigma model.Comment: 69 pages, v2: new "hybrid" equations for YQ-functions, figures and
tables are added. Analyticity of Y-system is discussed, v3: published versio
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