7,872 research outputs found
Incomplete graphical model inference via latent tree aggregation
Graphical network inference is used in many fields such as genomics or
ecology to infer the conditional independence structure between variables, from
measurements of gene expression or species abundances for instance. In many
practical cases, not all variables involved in the network have been observed,
and the samples are actually drawn from a distribution where some variables
have been marginalized out. This challenges the sparsity assumption commonly
made in graphical model inference, since marginalization yields locally dense
structures, even when the original network is sparse. We present a procedure
for inferring Gaussian graphical models when some variables are unobserved,
that accounts both for the influence of missing variables and the low density
of the original network. Our model is based on the aggregation of spanning
trees, and the estimation procedure on the Expectation-Maximization algorithm.
We treat the graph structure and the unobserved nodes as missing variables and
compute posterior probabilities of edge appearance. To provide a complete
methodology, we also propose several model selection criteria to estimate the
number of missing nodes. A simulation study and an illustration flow cytometry
data reveal that our method has favorable edge detection properties compared to
existing graph inference techniques. The methods are implemented in an R
package
Query-based Deep Improvisation
In this paper we explore techniques for generating new music using a
Variational Autoencoder (VAE) neural network that was trained on a corpus of
specific style. Instead of randomly sampling the latent states of the network
to produce free improvisation, we generate new music by querying the network
with musical input in a style different from the training corpus. This allows
us to produce new musical output with longer-term structure that blends aspects
of the query to the style of the network. In order to control the level of this
blending we add a noisy channel between the VAE encoder and decoder using
bit-allocation algorithm from communication rate-distortion theory. Our
experiments provide new insight into relations between the representational and
structural information of latent states and the query signal, suggesting their
possible use for composition purposes
Followers Are Not Enough: A Question-Oriented Approach to Community Detection in Online Social Networks
Community detection in online social networks is typically based on the
analysis of the explicit connections between users, such as "friends" on
Facebook and "followers" on Twitter. But online users often have hundreds or
even thousands of such connections, and many of these connections do not
correspond to real friendships or more generally to accounts that users
interact with. We claim that community detection in online social networks
should be question-oriented and rely on additional information beyond the
simple structure of the network. The concept of 'community' is very general,
and different questions such as "whom do we interact with?" and "with whom do
we share similar interests?" can lead to the discovery of different social
groups. In this paper we focus on three types of communities beyond structural
communities: activity-based, topic-based, and interaction-based. We analyze a
Twitter dataset using three different weightings of the structural network
meant to highlight these three community types, and then infer the communities
associated with these weightings. We show that the communities obtained in the
three weighted cases are highly different from each other, and from the
communities obtained by considering only the unweighted structural network. Our
results confirm that asking a precise question is an unavoidable first step in
community detection in online social networks, and that different questions can
lead to different insights about the network under study.Comment: 22 pages, 4 figures, 1 table
Learning on Graphs with Out-of-Distribution Nodes
Graph Neural Networks (GNNs) are state-of-the-art models for performing
prediction tasks on graphs. While existing GNNs have shown great performance on
various tasks related to graphs, little attention has been paid to the scenario
where out-of-distribution (OOD) nodes exist in the graph during training and
inference. Borrowing the concept from CV and NLP, we define OOD nodes as nodes
with labels unseen from the training set. Since a lot of networks are
automatically constructed by programs, real-world graphs are often noisy and
may contain nodes from unknown distributions. In this work, we define the
problem of graph learning with out-of-distribution nodes. Specifically, we aim
to accomplish two tasks: 1) detect nodes which do not belong to the known
distribution and 2) classify the remaining nodes to be one of the known
classes. We demonstrate that the connection patterns in graphs are informative
for outlier detection, and propose Out-of-Distribution Graph Attention Network
(OODGAT), a novel GNN model which explicitly models the interaction between
different kinds of nodes and separate inliers from outliers during feature
propagation. Extensive experiments show that OODGAT outperforms existing
outlier detection methods by a large margin, while being better or comparable
in terms of in-distribution classification.Comment: Accepted by KDD'2
Uncovering latent structure in valued graphs: A variational approach
As more and more network-structured data sets are available, the statistical
analysis of valued graphs has become common place. Looking for a latent
structure is one of the many strategies used to better understand the behavior
of a network. Several methods already exist for the binary case. We present a
model-based strategy to uncover groups of nodes in valued graphs. This
framework can be used for a wide span of parametric random graphs models and
allows to include covariates. Variational tools allow us to achieve approximate
maximum likelihood estimation of the parameters of these models. We provide a
simulation study showing that our estimation method performs well over a broad
range of situations. We apply this method to analyze host--parasite interaction
networks in forest ecosystems.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS361 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Latent Embeddings for Collective Activity Recognition
Rather than simply recognizing the action of a person individually,
collective activity recognition aims to find out what a group of people is
acting in a collective scene. Previ- ous state-of-the-art methods using
hand-crafted potentials in conventional graphical model which can only define a
limited range of relations. Thus, the complex structural de- pendencies among
individuals involved in a collective sce- nario cannot be fully modeled. In
this paper, we overcome these limitations by embedding latent variables into
feature space and learning the feature mapping functions in a deep learning
framework. The embeddings of latent variables build a global relation
containing person-group interac- tions and richer contextual information by
jointly modeling broader range of individuals. Besides, we assemble atten- tion
mechanism during embedding for achieving more com- pact representations. We
evaluate our method on three col- lective activity datasets, where we
contribute a much larger dataset in this work. The proposed model has achieved
clearly better performance as compared to the state-of-the- art methods in our
experiments.Comment: 6pages, accepted by IEEE-AVSS201
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