129,638 research outputs found
Unbiased sampling of network ensembles
Sampling random graphs with given properties is a key step in the analysis of
networks, as random ensembles represent basic null models required to identify
patterns such as communities and motifs. An important requirement is that the
sampling process is unbiased and efficient. The main approaches are
microcanonical, i.e. they sample graphs that match the enforced constraints
exactly. Unfortunately, when applied to strongly heterogeneous networks (like
most real-world examples), the majority of these approaches become biased
and/or time-consuming. Moreover, the algorithms defined in the simplest cases,
such as binary graphs with given degrees, are not easily generalizable to more
complicated ensembles. Here we propose a solution to the problem via the
introduction of a "Maximize and Sample" ("Max & Sam" for short) method to
correctly sample ensembles of networks where the constraints are `soft', i.e.
realized as ensemble averages. Our method is based on exact maximum-entropy
distributions and is therefore unbiased by construction, even for strongly
heterogeneous networks. It is also more computationally efficient than most
microcanonical alternatives. Finally, it works for both binary and weighted
networks with a variety of constraints, including combined degree-strength
sequences and full reciprocity structure, for which no alternative method
exists. Our canonical approach can in principle be turned into an unbiased
microcanonical one, via a restriction to the relevant subset. Importantly, the
analysis of the fluctuations of the constraints suggests that the
microcanonical and canonical versions of all the ensembles considered here are
not equivalent. We show various real-world applications and provide a code
implementing all our algorithms.Comment: MatLab code available at
http://www.mathworks.it/matlabcentral/fileexchange/46912-max-sam-package-zi
Exponential Family Matrix Completion under Structural Constraints
We consider the matrix completion problem of recovering a structured matrix
from noisy and partial measurements. Recent works have proposed tractable
estimators with strong statistical guarantees for the case where the underlying
matrix is low--rank, and the measurements consist of a subset, either of the
exact individual entries, or of the entries perturbed by additive Gaussian
noise, which is thus implicitly suited for thin--tailed continuous data.
Arguably, common applications of matrix completion require estimators for (a)
heterogeneous data--types, such as skewed--continuous, count, binary, etc., (b)
for heterogeneous noise models (beyond Gaussian), which capture varied
uncertainty in the measurements, and (c) heterogeneous structural constraints
beyond low--rank, such as block--sparsity, or a superposition structure of
low--rank plus elementwise sparseness, among others. In this paper, we provide
a vastly unified framework for generalized matrix completion by considering a
matrix completion setting wherein the matrix entries are sampled from any
member of the rich family of exponential family distributions; and impose
general structural constraints on the underlying matrix, as captured by a
general regularizer . We propose a simple convex regularized
--estimator for the generalized framework, and provide a unified and novel
statistical analysis for this general class of estimators. We finally
corroborate our theoretical results on simulated datasets.Comment: 20 pages, 9 figure
Task Selection for Bandit-Based Task Assignment in Heterogeneous Crowdsourcing
Task selection (picking an appropriate labeling task) and worker selection
(assigning the labeling task to a suitable worker) are two major challenges in
task assignment for crowdsourcing. Recently, worker selection has been
successfully addressed by the bandit-based task assignment (BBTA) method, while
task selection has not been thoroughly investigated yet. In this paper, we
experimentally compare several task selection strategies borrowed from active
learning literature, and show that the least confidence strategy significantly
improves the performance of task assignment in crowdsourcing.Comment: arXiv admin note: substantial text overlap with arXiv:1507.0580
A Robust Information Source Estimator with Sparse Observations
In this paper, we consider the problem of locating the information source
with sparse observations. We assume that a piece of information spreads in a
network following a heterogeneous susceptible-infected-recovered (SIR) model
and that a small subset of infected nodes are reported, from which we need to
find the source of the information. We adopt the sample path based estimator
developed in [1], and prove that on infinite trees, the sample path based
estimator is a Jordan infection center with respect to the set of observed
infected nodes. In other words, the sample path based estimator minimizes the
maximum distance to observed infected nodes. We further prove that the distance
between the estimator and the actual source is upper bounded by a constant
independent of the number of infected nodes with a high probability on infinite
trees. Our simulations on tree networks and real world networks show that the
sample path based estimator is closer to the actual source than several other
algorithms
Learning the Joint Representation of Heterogeneous Temporal Events for Clinical Endpoint Prediction
The availability of a large amount of electronic health records (EHR)
provides huge opportunities to improve health care service by mining these
data. One important application is clinical endpoint prediction, which aims to
predict whether a disease, a symptom or an abnormal lab test will happen in the
future according to patients' history records. This paper develops deep
learning techniques for clinical endpoint prediction, which are effective in
many practical applications. However, the problem is very challenging since
patients' history records contain multiple heterogeneous temporal events such
as lab tests, diagnosis, and drug administrations. The visiting patterns of
different types of events vary significantly, and there exist complex nonlinear
relationships between different events. In this paper, we propose a novel model
for learning the joint representation of heterogeneous temporal events. The
model adds a new gate to control the visiting rates of different events which
effectively models the irregular patterns of different events and their
nonlinear correlations. Experiment results with real-world clinical data on the
tasks of predicting death and abnormal lab tests prove the effectiveness of our
proposed approach over competitive baselines.Comment: 8 pages, this paper has been accepted by AAAI 201
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