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Delayed Sampling and Automatic Rao-Blackwellization of Probabilistic Programs

arXiv.org Machine Learning

We introduce a dynamic mechanism for the solution of analytically-tractable substructure in probabilistic programs, using conjugate priors and affine transformations to reduce variance in Monte Carlo estimators. For inference with Sequential Monte Carlo, this automatically yields improvements such as locally-optimal proposals and Rao-Blackwellization. The mechanism maintains a directed graph alongside the running program that evolves dynamically as operations are triggered upon it. Nodes of the graph represent random variables, edges the analytically-tractable relationships between them. Random variables remain in the graph for as long as possible, to be sampled only when they are used by the program in a way that cannot be resolved analytically. In the meantime, they are conditioned on as many observations as possible. We demonstrate the mechanism with a few pedagogical examples, as well as a linear-nonlinear state-space model with simulated data, and an epidemiological model with real data of a dengue outbreak in Micronesia. In all cases one or more variables are automatically marginalized out to significantly reduce variance in estimates of the marginal likelihood, in the final case facilitating a random-weight or pseudo-marginal-type importance sampler for parameter estimation. We have implemented the approach in Anglican and a new probabilistic programming language called Birch.


Bayesian Recurrent Neural Networks

arXiv.org Machine Learning

In this work we explore a straightforward variational Bayes scheme for Recurrent Neural Networks. Firstly, we show that a simple adaptation of truncated backpropagation through time can yield good quality uncertainty estimates and superior regularisation at only a small extra computational cost during training, also reducing the amount of parameters by 80\%. Secondly, we demonstrate how a novel kind of posterior approximation yields further improvements to the performance of Bayesian RNNs. We incorporate local gradient information into the approximate posterior to sharpen it around the current batch statistics. We show how this technique is not exclusive to recurrent neural networks and can be applied more widely to train Bayesian neural networks. We also empirically demonstrate how Bayesian RNNs are superior to traditional RNNs on a language modelling benchmark and an image captioning task, as well as showing how each of these methods improve our model over a variety of other schemes for training them. We also introduce a new benchmark for studying uncertainty for language models so future methods can be easily compared.


Incremental Learning-to-Learn with Statistical Guarantees

arXiv.org Machine Learning

In learning-to-learn the goal is to infer a learning algorithm that works well on a class of tasks sampled from an unknown meta distribution. In contrast to previous work on batch learning-to-learn, we consider a scenario where tasks are presented sequentially and the algorithm needs to adapt incrementally to improve its performance on future tasks. Key to this setting is for the algorithm to rapidly incorporate new observations into the model as they arrive, without keeping them in memory. We focus on the case where the underlying algorithm is ridge regression parameterized by a positive semidefinite matrix. We propose to learn this matrix by applying a stochastic strategy to minimize the empirical error incurred by ridge regression on future tasks sampled from the meta distribution. We study the statistical properties of the proposed algorithm and prove non-asymptotic bounds on its excess transfer risk, that is, the generalization performance on new tasks from the same meta distribution. We compare our online learning-to-learn approach with a state of the art batch method, both theoretically and empirically.


Expeditious Generation of Knowledge Graph Embeddings

arXiv.org Artificial Intelligence

Knowledge Graph Embedding methods aim at representing entities and relations in a knowledge base as points or vectors in a continuous vector space. Several approaches using embeddings have shown promising results on tasks such as link prediction, entity recommendation, question answering, and triplet classification. However, only a few methods can compute low-dimensional embeddings of very large knowledge bases. In this paper, we propose KG2Vec, a novel approach to Knowledge Graph Embedding based on the skip-gram model. Instead of using a predefined scoring function, we learn it relying on Long Short-Term Memories. We evaluated the goodness of our embeddings on knowledge graph completion and show that KG2Vec is comparable to the quality of the scalable state-of-the-art approaches and can process large graphs by parsing more than a hundred million triples in less than 6 hours on common hardware.


A Formalization of Kant's Second Formulation of the Categorical Imperative

arXiv.org Artificial Intelligence

We present a formalization and computational implementation of the second formulation of Kant's categorical imperative. This ethical principle requires an agent to never treat someone merely as a means but always also as an end. Here we interpret this principle in terms of how persons are causally affected by actions. We introduce Kantian causal agency models in which moral patients, actions, goals, and causal influence are represented, and we show how to formalize several readings of Kant's categorical imperative that correspond to Kant's concept of strict and wide duties towards oneself and others. Stricter versions handle cases where an action directly causally affects oneself or others, whereas the wide version maximizes the number of persons being treated as an end. We discuss limitations of our formalization by pointing to one of Kant's cases that the machinery cannot handle in a satisfying way.


Counterfactual Explanations without Opening the Black Box: Automated Decisions and the GDPR

arXiv.org Artificial Intelligence

There has been much discussion of the right to explanation in the EU General Data Protection Regulation, and its existence, merits, and disadvantages. Implementing a right to explanation that opens the black box of algorithmic decision-making faces major legal and technical barriers. Explaining the functionality of complex algorithmic decision-making systems and their rationale in specific cases is a technically challenging problem. Some explanations may offer little meaningful information to data subjects, raising questions around their value. Explanations of automated decisions need not hinge on the general public understanding how algorithmic systems function. Even though such interpretability is of great importance and should be pursued, explanations can, in principle, be offered without opening the black box. Looking at explanations as a means to help a data subject act rather than merely understand, one could gauge the scope and content of explanations according to the specific goal or action they are intended to support. From the perspective of individuals affected by automated decision-making, we propose three aims for explanations: (1) to inform and help the individual understand why a particular decision was reached, (2) to provide grounds to contest the decision if the outcome is undesired, and (3) to understand what would need to change in order to receive a desired result in the future, based on the current decision-making model. We assess how each of these goals finds support in the GDPR. We suggest data controllers should offer a particular type of explanation, unconditional counterfactual explanations, to support these three aims. These counterfactual explanations describe the smallest change to the world that can be made to obtain a desirable outcome, or to arrive at the closest possible world, without needing to explain the internal logic of the system.


Facebook Was Letting Down Users Years Before Cambridge Analytica

Slate

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society. It sounds like the stuff of spy novels. A secretive company backed by an eccentric billionaire taps into sensitive data gathered by a University of Cambridge researcher. The company then works to help elect an ultranationalist presidential candidate who admires Russian President Vladimir Putin. Oh, and that Cambridge researcher, Aleksandr Kogan, worked briefly for St. Petersburg State University.


Madrid Advanced Statistics and Data Mining Summer School

@machinelearnbot

The Madrid ASDM summer school is in its thirteenth edition this year, with hundreds of students from all over the world having attended so far. It comprises 12 intensive (15 lecture hours) week-long courses, and a student may attend from one up to six courses. The courses cover topics such as Neural Networks and Deep Learning, Bayesian Networks, Big Data with Apache Spark, Bayesian Inference, Text Mining and Time Series. Each course has theoretical and practical classes, the latter done with R or python. While the summer school is mainly attended by people from academia - PhD students and researchers-, people from the industry also assist.


'4D printing' is the catchphrase, programmable materials the newsmakers

@machinelearnbot

If you've been following 3D printing in recent years, you may have come across a "next new thing" that sounds like it was dreamed up for the twilight zone: 4D printing, so dubbed and promoted by Skylar Tibbits, director of MIT's Self-Assembly Lab. You unlock this technology, as Rod Serling would say, with the keys of chemistry, physics, engineering and materials science, and move into a realm of both molecular properties and computer-aided design (CAD). Then you cross over into programmable materials -- and that's the term that leads to most of the news made in this field since 2014. Once they're produced on 3D printers, objects made of programmable materials continue to take shape, folding, unfolding or assembling themselves in response to outside stimuli such as light, movement, heat, pressure or water. Tibbits' TED Talk videos demonstrate multimaterial, printed 2D strands that curl themselves into the letters "MIT," and printed flat sheets of programmable materials that, once robotically cut, transform themselves into shoes. Tibbits said 4D printing started as a way to "print" robots, but taking out all the electromechanical systems.


Artificial Intelligence in Healthcare Conference: Improving system efficiency

#artificialintelligence

We have a great opportunity to get smarter about the way we are using AI and machine learning with datasets to improve the quality of clinical care" - Simon Stevens, chief executive of NHS England The adoption of artificial intelligence in healthcare is on the rise and is solving a variety of problems for patients, hospitals and the healthcare industry overall. Sir John Bell's Life Sciences Industrial strategy identified the faster application of Artificial Intelligence (AI) as a priority and the NHS England is to invest more in AI over the next 12 months and create new Digital Innovation Hubs. These new Digital Innovation Hubs will enable researchers to engage with a meaningful dataset. AI is increasingly being applied in healthcare and medicine, with the greatest impact being achieved thus far in medical imaging. A recent Lancet editorial entitled'Augmenting diagnostic vision with AI' suggested artificial intelligence had the potential to interpret clinical data more accurately and more rapidly than medical specialists', such as radiologist and dermatologist who analyse hundreds of thousands of images over their career.