9,720 research outputs found
Revisiting Precision and Recall Definition for Generative Model Evaluation
In this article we revisit the definition of Precision-Recall (PR) curves for
generative models proposed by Sajjadi et al. (arXiv:1806.00035). Rather than
providing a scalar for generative quality, PR curves distinguish mode-collapse
(poor recall) and bad quality (poor precision). We first generalize their
formulation to arbitrary measures, hence removing any restriction to finite
support. We also expose a bridge between PR curves and type I and type II error
rates of likelihood ratio classifiers on the task of discriminating between
samples of the two distributions. Building upon this new perspective, we
propose a novel algorithm to approximate precision-recall curves, that shares
some interesting methodological properties with the hypothesis testing
technique from Lopez-Paz et al (arXiv:1610.06545). We demonstrate the interest
of the proposed formulation over the original approach on controlled
multi-modal datasets.Comment: ICML 201
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Learning from the learners' experience: e-Learning@greenwich post-conference reflections
This publication comprises papers from presenters who, having made a conference presentation, were invited to author an academic paper about their work
Regional economic impacts of a plant disease incursion using a general equilibrium approach
The present study uses a dynamic multiregional computable general equilibrium (CGE) model to estimate the micro- andmacroeconomic effects of a hypothetical disease or pest outbreak. Our example is a Karnal bunt incursion in wheat in Western Australia. The extent of the incursion, the impact of the disease or pest on plant yields, the response of buyers, the costs of eradication and the time path of the scenario contribute to outcomes at the industry, regional, state and national levels. We decompose the contribution of these individual direct effects to the overall impact of the incursion. This might provide some guidance regarding areas for priority in attempting to eradicate or minimise the impacts of a disease or pest. The study also introduces a theory of dynamic regional labour adjustment in which economic events may lead to both real wage differentials and worker migration between regions.Crop Production/Industries,
Training Behavior of Sparse Neural Network Topologies
Improvements in the performance of deep neural networks have often come
through the design of larger and more complex networks. As a result, fast
memory is a significant limiting factor in our ability to improve network
performance. One approach to overcoming this limit is the design of sparse
neural networks, which can be both very large and efficiently trained. In this
paper we experiment training on sparse neural network topologies. We test
pruning-based topologies, which are derived from an initially dense network
whose connections are pruned, as well as RadiX-Nets, a class of network
topologies with proven connectivity and sparsity properties. Results show that
sparse networks obtain accuracies comparable to dense networks, but extreme
levels of sparsity cause instability in training, which merits further study.Comment: 6 pages. Presented at the 2019 IEEE High Performance Extreme
Computing (HPEC) Conference. Received "Best Paper" awar
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Comparison of Bayesian and frequentist group-sequential clinical trial designs
Background: There is a growing interest in the use of Bayesian adaptive designs in late-phase clinical trials. This
includes the use of stopping rules based on Bayesian analyses in which the frequentist type I error rate is controlled as
in frequentist group-sequential designs.
Methods: This paper presents a practical comparison of Bayesian and frequentist group-sequential tests. Focussing
on the setting in which data can be summarised by normally distributed test statistics, we evaluate and compare
boundary values and operating characteristics.
Results: Although Bayesian and frequentist group-sequential approaches are based on fundamentally different
paradigms, in a single arm trial or two-arm comparative trial with a prior distribution specified for the treatment
difference, Bayesian and frequentist group-sequential tests can have identical stopping rules if particular critical values
with which the posterior probability is compared or particular spending function values are chosen. If the Bayesian
critical values at different looks are restricted to be equal, OāBrien and Flemingās design corresponds to a Bayesian
design with an exceptionally informative negative prior, Pocockās design to a Bayesian design with a non-informative
prior and frequentist designs with a linear alpha spending function are very similar to Bayesian designs with slightly
informative priors.
This contrasts with the setting of a comparative trial with independent prior distributions specified for treatment
effects in different groups. In this case Bayesian and frequentist group-sequential tests cannot have the same
stopping rule as the Bayesian stopping rule depends on the observed means in the two groups and not just on their
difference. In this setting the Bayesian test can only be guaranteed to control the type I error for a specified range of
values of the control group treatment effect.
Conclusions: Comparison of frequentist and Bayesian designs can encourage careful thought about design
parameters and help to ensure appropriate design choices are made
Molecular recognition and its underlying mechanisms in molecularly imprinted polymers
Molecular recognition in molecularly imprinting polymers (MIPs) is governed by two mechanisms: pre-organization of functional groups and shape specificity of the binding site. While pre-organization of functional groups has been studied extensively, shape specificity of the binding site has not been rigorously explored. The goal of this research is to determine the influence of shape specificity on molecular recognition in MIPs (Chapter 2). Once shape selectivity was proven to play a vital role in molecular recognition, it was important to determine if pre-organization of functional groups or shape specificity was the dominating factor in determining molecular recognition in the binding site (Chapter 3). Chapters 4 and 5 contain research that is not directly related to shape selectivity or pre-organization of functional groups in MIPs, but is nevertheless important to the field of molecular imprinting and synthetic methodology. A survey of commercially available basic functional monomers was conducted with the goal of making MIPs with acidic compounds as templates. The effect of particle size and flow rate on binding selectivity was investigated for both classic ethylene glycol dimethacrylate (EGDMA)/methacrylic acid (MAA) MIPs and new 2-(methacryloylamine)ethyl-2-methacrylate (NOBE) MIPs. Thin-layer and centrifugally accelerated radial chromatographic experiments were done with MIPs as the stationary phase. A preliminary investigation into the use of quaternary ammonium salts as templates in MIP experiments was conducted. Synthetic methodology involving palladium catalyzed cross couplings is detailed in Chapter 5
Graham Huggan. Territorial Disputes: Maps and Mapping Strategies in Contemporary Canadian and Australian Fiction
Auctions with Options to Re-auction
We examine a dynamic model of English auctions with independent private values. There is a single object for sale and it is not possible for the seller, who has a value of zero for the object, to commit not to sell in the future if a sale is not accomplished today. The seller may be able to commit to a reserve price, or make a cheap-talk announcement of a reserve price and secretly bid for the object herself in order to re-auction it in a later round with a new set of bidders. Bidders are "short-lived" in the sense that at the end of each round all existing bidders vanish and new bidders start arriving. This framework allows us to obtain existing results for one shot-auctions as special cases. This framework also allows us to capture some of the features of thick internet auctions and to obtain some new insights on the role of commitment, on optimal length and on socially optimal reserve prices that are not apparent from a one-shot auction perspective.
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