7,920 research outputs found
Learning without Recall: A Case for Log-Linear Learning
We analyze a model of learning and belief formation in networks in which
agents follow Bayes rule yet they do not recall their history of past
observations and cannot reason about how other agents' beliefs are formed. They
do so by making rational inferences about their observations which include a
sequence of independent and identically distributed private signals as well as
the beliefs of their neighboring agents at each time. Fully rational agents
would successively apply Bayes rule to the entire history of observations. This
leads to forebodingly complex inferences due to lack of knowledge about the
global network structure that causes those observations. To address these
complexities, we consider a Learning without Recall model, which in addition to
providing a tractable framework for analyzing the behavior of rational agents
in social networks, can also provide a behavioral foundation for the variety of
non-Bayesian update rules in the literature. We present the implications of
various choices for time-varying priors of such agents and how this choice
affects learning and its rate.Comment: in 5th IFAC Workshop on Distributed Estimation and Control in
Networked Systems, (NecSys 2015
Spectral Clustering for Optical Confirmation and Redshift Estimation of X-ray Selected Galaxy Cluster Candidates in the SDSS Stripe 82
We develop a galaxy cluster finding algorithm based on spectral clustering
technique to identify optical counterparts and estimate optical redshifts for
X-ray selected cluster candidates. As an application, we run our algorithm on a
sample of X-ray cluster candidates selected from the third XMM-Newton
serendipitous source catalog (3XMM-DR5) that are located in the Stripe 82 of
the Sloan Digital Sky Survey (SDSS). Our method works on galaxies described in
the color-magnitude feature space. We begin by examining 45 galaxy clusters
with published spectroscopic redshifts in the range of 0.1 to 0.8 with a median
of 0.36. As a result, we are able to identify their optical counterparts and
estimate their photometric redshifts, which have a typical accuracy of 0.025
and agree with the published ones. Then, we investigate another 40 X-ray
cluster candidates (from the same cluster survey) with no redshift information
in the literature and found that 12 candidates are considered as galaxy
clusters in the redshift range from 0.29 to 0.76 with a median of 0.57. These
systems are newly discovered clusters in X-rays and optical data. Among them 7
clusters have spectroscopic redshifts for at least one member galaxy.Comment: 15 pages, 7 figures, 3 tables, 1 appendix, Accepted by Journal of
"Astronomy and Computing
Learning without Recall by Random Walks on Directed Graphs
We consider a network of agents that aim to learn some unknown state of the
world using private observations and exchange of beliefs. At each time, agents
observe private signals generated based on the true unknown state. Each agent
might not be able to distinguish the true state based only on her private
observations. This occurs when some other states are observationally equivalent
to the true state from the agent's perspective. To overcome this shortcoming,
agents must communicate with each other to benefit from local observations. We
propose a model where each agent selects one of her neighbors randomly at each
time. Then, she refines her opinion using her private signal and the prior of
that particular neighbor. The proposed rule can be thought of as a Bayesian
agent who cannot recall the priors based on which other agents make inferences.
This learning without recall approach preserves some aspects of the Bayesian
inference while being computationally tractable. By establishing a
correspondence with a random walk on the network graph, we prove that under the
described protocol, agents learn the truth exponentially fast in the almost
sure sense. The asymptotic rate is expressed as the sum of the relative
entropies between the signal structures of every agent weighted by the
stationary distribution of the random walk.Comment: 6 pages, To Appear in Conference on Decision and Control 201
Complexity and Behind the Horizon Cut Off
Motivated by deformation of a conformal field theory we
compute holographic complexity for a black brane solution with a cut off using
"complexity=action" proposal. In order to have a late time behavior consistent
with Lloyd's bound one is forced to have a cut off behind the horizon whose
value is fixed by the boundary cut off. Using this result we compute
holographic complexity for two dimensional AdS solutions where we get expected
late times linear growth. It is in contrast with the naively computation which
is done without assuming the cut off where the complexity approaches a constant
at the late time.Comment: 14 pages, 2 figures, refs added, contribution of a counter term is
added, minor correction, the final conclusion is not change
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