818 research outputs found
Invariance of Weight Distributions in Rectified MLPs
An interesting approach to analyzing neural networks that has received
renewed attention is to examine the equivalent kernel of the neural network.
This is based on the fact that a fully connected feedforward network with one
hidden layer, a certain weight distribution, an activation function, and an
infinite number of neurons can be viewed as a mapping into a Hilbert space. We
derive the equivalent kernels of MLPs with ReLU or Leaky ReLU activations for
all rotationally-invariant weight distributions, generalizing a previous result
that required Gaussian weight distributions. Additionally, the Central Limit
Theorem is used to show that for certain activation functions, kernels
corresponding to layers with weight distributions having mean and finite
absolute third moment are asymptotically universal, and are well approximated
by the kernel corresponding to layers with spherical Gaussian weights. In deep
networks, as depth increases the equivalent kernel approaches a pathological
fixed point, which can be used to argue why training randomly initialized
networks can be difficult. Our results also have implications for weight
initialization.Comment: ICML 201
Bayesian Inference in Estimation of Distribution Algorithms
Metaheuristics such as Estimation of Distribution Algorithms and the Cross-Entropy method use probabilistic modelling and inference to generate candidate solutions in optimization problems. The model fitting task in this class of algorithms has largely been carried out to date based on maximum likelihood. An alternative approach that is prevalent in statistics and machine learning is to use Bayesian inference. In this paper, we provide a framework for the application of Bayesian inference techniques in probabilistic model-based optimization. Based on this framework, a simple continuous Bayesian Estimation of Distribution Algorithm is described. We evaluate and compare this algorithm experimentally with its maximum likelihood equivalent, UMDAG c
Unsupervised DRG upcoding detection in healthcare databases
Diagnosis Related Group (DRG) upcoding is an anomaly in healthcare data that costs hundreds of millions of dollars in many developed countries. DRG upcoding is typically detected through resource intensive auditing. As supervised modeling of DRG upcoding is severely constrained by scope and timeliness of past audit data, we propose in this paper an unsupervised algorithm to filter data for potential identification of DRG upcoding. The algorithm has been applied to a hip replacement/revision dataset and a heart-attack dataset. The results are consistent with the assumptions held by domain experts
Examining average and discounted reward optimality criteria in reinforcement learning
In reinforcement learning (RL), the goal is to obtain an optimal policy, for
which the optimality criterion is fundamentally important. Two major optimality
criteria are average and discounted rewards, where the later is typically
considered as an approximation to the former. While the discounted reward is
more popular, it is problematic to apply in environments that have no natural
notion of discounting. This motivates us to revisit a) the progression of
optimality criteria in dynamic programming, b) justification for and
complication of an artificial discount factor, and c) benefits of directly
maximizing the average reward. Our contributions include a thorough examination
of the relationship between average and discounted rewards, as well as a
discussion of their pros and cons in RL. We emphasize that average-reward RL
methods possess the ingredient and mechanism for developing the general
discounting-free optimality criterion (Veinott, 1969) in RL.Comment: 14 pages, 3 figures, 10-page main conten
Modularity based linkage model for neuroevolution
Crossover between neural networks is considered disruptive due to the strong
functional dependency between connection weights. We propose a modularity-based
linkage model at the weight level to preserve functionally dependent
communities (building blocks) in neural networks during mixing. A proximity
matrix is built by estimating the dependency between weights, then a community
detection algorithm maximizing modularity is run on the graph described by such
matrix. The resulting communities/groups of parameters are considered to be
mutually independent and used as crossover masks in an optimal mixing EA. A
variant is tested with an operator that neutralizes the permutation problem of
neural networks to a degree. Experiments were performed on 8 and 10-bit parity
problems as the intrinsic hierarchical nature of the dependencies in these
problems are challenging to learn. The results show that our algorithm finds
better, more functionally dependent linkage which leads to more successful
crossover and better performance
Population-based continuous optimization, probabilistic modelling and mean shift
Evolutionary algorithms perform optimization using a population of sample solution points. An interesting development has been to view population-based optimization as the process of evolving an explicit, probabilistic model of the search space. This paper investigates a formal basis for continuous, population-based optimization in terms of a stochastic gradient descent on the Kullback-Leibler divergence between the model probability density and the objective function, represented as an unknown density of assumed form. This leads to an update rule that is related and compared with previous theoretical work, a continuous version of the population-based incremental learning algorithm, and the generalized mean shift clustering framework. Experimental results are presented that demonstrate the dynamics of the new algorithm on a set of simple test problems
Framework for software architecture visualization assessment.
In order to assess software architecture visualisation strategies, we qualitatively characterize then construct an assessment framework with 7 key areas and 31 features. The framework is used for evaluation and comparison of various strategies from multiple stakeholder perspectives. Six existing software architecture visualisation tools and a seventh research tool were evaluated. All
tools exhibited shortcomings when evaluated in the framework
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