6,377 research outputs found
New Alignment Methods for Discriminative Book Summarization
We consider the unsupervised alignment of the full text of a book with a
human-written summary. This presents challenges not seen in other text
alignment problems, including a disparity in length and, consequent to this, a
violation of the expectation that individual words and phrases should align,
since large passages and chapters can be distilled into a single summary
phrase. We present two new methods, based on hidden Markov models, specifically
targeted to this problem, and demonstrate gains on an extractive book
summarization task. While there is still much room for improvement,
unsupervised alignment holds intrinsic value in offering insight into what
features of a book are deemed worthy of summarization.Comment: This paper reflects work in progres
An Empirical Comparison of Parsing Methods for Stanford Dependencies
Stanford typed dependencies are a widely desired representation of natural
language sentences, but parsing is one of the major computational bottlenecks
in text analysis systems. In light of the evolving definition of the Stanford
dependencies and developments in statistical dependency parsing algorithms,
this paper revisits the question of Cer et al. (2010): what is the tradeoff
between accuracy and speed in obtaining Stanford dependencies in particular? We
also explore the effects of input representations on this tradeoff:
part-of-speech tags, the novel use of an alternative dependency representation
as input, and distributional representaions of words. We find that direct
dependency parsing is a more viable solution than it was found to be in the
past. An accompanying software release can be found at:
http://www.ark.cs.cmu.edu/TBSDComment: 13 pages, 2 figure
Coalescent histories for lodgepole species trees
Coalescent histories are combinatorial structures that describe for a given
gene tree and species tree the possible lists of branches of the species tree
on which the gene tree coalescences take place. Properties of the number of
coalescent histories for gene trees and species trees affect a variety of
probabilistic calculations in mathematical phylogenetics. Exact and asymptotic
evaluations of the number of coalescent histories, however, are known only in a
limited number of cases. Here we introduce a particular family of species
trees, the \emph{lodgepole} species trees , in which
tree has taxa. We determine the number of coalescent
histories for the lodgepole species trees, in the case that the gene tree
matches the species tree, showing that this number grows with in the
number of taxa . This computation demonstrates the existence of tree
families in which the growth in the number of coalescent histories is faster
than exponential. Further, it provides a substantial improvement on the lower
bound for the ratio of the largest number of matching coalescent histories to
the smallest number of matching coalescent histories for trees with taxa,
increasing a previous bound of
to . We discuss the implications of our
enumerative results for phylogenetic computations
Detailed analysis of the predictions of loop quantum cosmology for the primordial power spectra
We provide an exhaustive numerical exploration of the predictions of loop
quantum cosmology (LQC) with a post-bounce phase of inflation for the
primordial power spectrum of scalar and tensor perturbations. We extend
previous analysis by characterizing the phenomenologically relevant parameter
space and by constraining it using observations. Furthermore, we characterize
the shape of LQC-corrections to observable quantities across this parameter
space. Our analysis provides a framework to contrast more accurately the theory
with forthcoming polarization data, and it also paves the road for the
computation of other observables beyond the power spectra, such as
non-Gaussianity.Comment: 24 pages, 5 figure
On the number of ranked species trees producing anomalous ranked gene trees
Analysis of probability distributions conditional on species trees has
demonstrated the existence of anomalous ranked gene trees (ARGTs), ranked gene
trees that are more probable than the ranked gene tree that accords with the
ranked species tree. Here, to improve the characterization of ARGTs, we study
enumerative and probabilistic properties of two classes of ranked labeled
species trees, focusing on the presence or avoidance of certain subtree
patterns associated with the production of ARGTs. We provide exact enumerations
and asymptotic estimates for cardinalities of these sets of trees, showing that
as the number of species increases without bound, the fraction of all ranked
labeled species trees that are ARGT-producing approaches 1. This result extends
beyond earlier existence results to provide a probabilistic claim about the
frequency of ARGTs
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