Approximating Likelihood Ratios with Calibrated Discriminative Classifiers

In many fields of science, generalized likelihood ratio tests are established tools for statistical inference. At the same time, it has become increasingly common that a simulator (or generative model) is used to describe complex processes that tie parameters $\theta$ of an underlying theory and measurement apparatus to high-dimensional observations $\mathbf{x}\in \mathbb{R}^p$. However, simulator often do not provide a way to evaluate the likelihood function for a given observation $\mathbf{x}$, which motivates a new class of likelihood-free inference algorithms. In this paper, we show that likelihood ratios are invariant under a specific class of dimensionality reduction maps $\mathbb{R}^p \mapsto \mathbb{R}$. As a direct consequence, we show that discriminative classifiers can be used to approximate the generalized likelihood ratio statistic when only a generative model for the data is available. This leads to a new machine learning-based approach to likelihood-free inference that is complementary to Approximate Bayesian Computation, and which does not require a prior on the model parameters. Experimental results on artificial problems with known exact likelihoods illustrate the potential of the proposed method.Comment: 35 pages, 5 figure

Mining gold from implicit models to improve likelihood-free inference

Simulators often provide the best description of real-world phenomena. However, they also lead to challenging inverse problems because the density they implicitly define is often intractable. We present a new suite of simulation-based inference techniques that go beyond the traditional Approximate Bayesian Computation approach, which struggles in a high-dimensional setting, and extend methods that use surrogate models based on neural networks. We show that additional information, such as the joint likelihood ratio and the joint score, can often be extracted from simulators and used to augment the training data for these surrogate models. Finally, we demonstrate that these new techniques are more sample efficient and provide higher-fidelity inference than traditional methods.Comment: Code available at https://github.com/johannbrehmer/simulator-mining-example . v2: Fixed typos. v3: Expanded discussion, added Lotka-Volterra example. v4: Improved clarit

Resistance to garbage and dynamics of territorialization through the use of exposed writing

Este texto ofrece una caracterización empírica de una dinámica de resistencia a la presencia de basura en el espacio público y a la contaminación observable actualmente en un barrio pericentral de la ciudad de Santiago de Chile. El foco de análisis está puesto en las inscripciones gráficas, en el entendido de que, a través de ellas, los habitantes enfrentan el problema indicado activando nuevas dinámicas de territorialización y generando nuevas formas de dar inteligibilidad al barrio y a los sujetos que lo habitan. La información empleada fue generada mediante un procedimiento de catastro sistemático de las inscripciones gráficas del barrio, su registro fotográfico y georreferenciación, para hacer viable un análisis pragmático, tanto de su contenido como de su emplazamiento, con base en los conceptos de la antropología de las escrituras urbanas expuestas. El artículo entrega una comprensión sistemática de la relevancia de prácticas, usualmente banalizadas, mediante las cuales los habitantes despliegan formas de resistencia a la desposesión territorial y epistémica que afecta a los territorios del capitalismo urbano actual.This text presents an empirical characterization of a resistance dynamic to the presence of garbage in the public space and the contamination currently seen in a peri-central neighborhood of Santiago de Chile. The focus of the analysis is placed on the street writing, understanding that the inhabitants, through these, face this problem, activating new dynamics of territorialization and generating new ways of providing intelligibility to the neighborhood and to the subjects living there. The information was generated through a systemic listing of the neighborhood’s street writing, its photographic record and geo-referencing, to make a pragmatic analysis viable, both of its content and its location, based on the anthropological concepts of the exposed urban writing. The article provides a systematic understanding of the relevance of practices, usually trivialized, by which inhabitants display means of resistance to territorial and epistemic dispossession that affect the territories of the current urban capitalism

A Guide to Constraining Effective Field Theories with Machine Learning

We develop, discuss, and compare several inference techniques to constrain theory parameters in collider experiments. By harnessing the latent-space structure of particle physics processes, we extract extra information from the simulator. This augmented data can be used to train neural networks that precisely estimate the likelihood ratio. The new methods scale well to many observables and high-dimensional parameter spaces, do not require any approximations of the parton shower and detector response, and can be evaluated in microseconds. Using weak-boson-fusion Higgs production as an example process, we compare the performance of several techniques. The best results are found for likelihood ratio estimators trained with extra information about the score, the gradient of the log likelihood function with respect to the theory parameters. The score also provides sufficient statistics that contain all the information needed for inference in the neighborhood of the Standard Model. These methods enable us to put significantly stronger bounds on effective dimension-six operators than the traditional approach based on histograms. They also outperform generic machine learning methods that do not make use of the particle physics structure, demonstrating their potential to substantially improve the new physics reach of the LHC legacy results.Comment: See also the companion publication "Constraining Effective Field Theories with Machine Learning" at arXiv:1805.00013, a brief introduction presenting the key ideas. The code for these studies is available at https://github.com/johannbrehmer/higgs_inference . v2: Added references. v3: Improved description of algorithms, added references. v4: Clarified text, added reference

La diversidad de especies de vivientes corpóreos a la luz de la filosofía de Santo Tomás de Aquino

Beyond the theories and ideologies that sometimes are presented as inevitably linked to it, the truth is that the fact of evolution of living species is a highly relevant theoretical framework in modern biology. Therefore, any attempt to establish a fruitful dialogue between biology and Thomistic philosophy must address this issue; in order to advance in that direction, however, one should answer first the question about the diversity of species of living beings, a controversial topic among Thomistic scholars. In this article we argue that the multiplicity of biological species is compatible and consistent with the metaphysical scheme proposed by Thomas Aquinas; moreover, we think that this thesis was suggested by Aquinas himself in some passages of his work, though certainly not in an evolutionary context. As Saint Thomas repeatedly points out, in most cases we do not know the specific difference included in the definition of these species. This, however, does not imply our absolute ignorance about them; we think, on the contrary, that the philosophical examination of vital operations may constitute a valid strategy for advancing, at least partially, in the distinction of certain species of corporeal living beings. In the final section of the article we apply this principle in the philosophical analysis of the criterion of interbreeding that biologists commonly use to develop their taxonomic classifications. Más allá de las teorías e ideologías que a veces se presentan como indisolublemente ligadas a él, lo cierto es que el hecho de la evolución de los seres vivos ha llegado a constituir un marco teórico sumamente relevante para la biología moderna. Un intento serio de establecer un diálogo fructífero entre la biología y la filosofía tomista, por lo tanto, debe enfrentar esta cuestión. Para avanzar en dicha dirección, empero, debe antes abordarse el interrogante referida a la diversidad específica de los vivientes, un tópico controversial entre los estudiosos del pensamiento de Tomás de Aquino. En este artículo argumentamos que la multiplicidad de especies biológicas es una tesis no solo compatible y consistente con el esquema metafísico tomista, sino que más aún, fue sugerida por el Aquinate en algunos pasajes de su obra, aunque no, por supuesto, en un contexto evolutivo. Como lo señala repetidamente Santo Tomás, en una mayoría de los casos desconocemos la diferencia específica incluida en la definición de estas especies. De ello, no obstante, no se sigue nuestra absoluta ignorancia al respecto; sostenemos, en cambio, que el examen filosófico de las operaciones vitales puede constituir una estrategia válida para avanzar, al menos parcialmente, en la distinción de ciertas especies de vivientes corpóreos. En la sección final del artículo aplicamos este principio para examinar filosóficamente el criterio de la interfecundidad que los biólogos utilizan frecuentemente para elaborar sus clasificaciones taxonómicas

Homonacionalismo e experiências de discriminação da comunidade gay migrante no Chile

El objetivo de este artículo es identificar y caracterizar las experiencias de discriminación que han tenido las personas extranjeras y que forman parte de la comunidad gay migrante en Chile, desde la perspectiva del homonacionalismo. El estudio se basa en las tensiones conceptuales entre la heteronorma y homonorma, poniendo particular énfasis a la emergencia de discursos nacionalistas al interior de la propia comunidad gay. La metodología ha sido de carácter cualitativo mediante cuestionario en línea autoadministrado con alcance de estudio de caso emblemático. Se concluye que los discursos de los participantes dan cuentan de experiencias de discriminación nacionalista a la hora de encuentros sociales y sexuales, así como también discriminación laboral.O objetivo deste artigo é identificar e caracterizar as experiências de discriminação vivenciadas por estrangeiros que fazem parte da comunidade LGBTIQA+ no Chile. O estudo baseia-se nas tensões conceituais entre heteronorma e homonorma, dando particular ênfase à emergência de discursos nacionalistas dentro da própria comunidade gay, ou homonacionalismo. A metodologia foi de natureza qualitativa através de um questionário online autoaplicável no âmbito de um estudo de caso emblemático. Conclui-se que as falas dos participantes dão conta de experiências de discriminação nacionalista no momento de encontros sociais e sexuais, bem como discriminação trabalhista