6,578 research outputs found

    Algebraic equivalence between certain models for superfluid--insulator transition

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    Algebraic contraction is proposed to realize mappings between models Hamiltonians. This transformation contracts the algebra of the degrees of freedom underlying the Hamiltonian. The rigorous mapping between the anisotropic XXZXXZ Heisenberg model, the Quantum Phase Model, and the Bose Hubbard Model is established as the contractions of the algebra u(2)u(2) underlying the dynamics of the XXZXXZ Heisenberg model.Comment: 5 pages, revte

    Reinventing the Dutch tax-benefit system; exploring the frontier of the equity-efficiency trade-off

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    European governments aim to raise labour supply, cut unemployment and, at the same time, maintain social cohesion. Yet, economists have stressed the trade-off between these objectives. This paper reviews the key policy insights from optimal tax theory to identify options for reform in the tax-benefit system that can potentially improve the equity-efficiency trade-off. Using a comprehensive applied general equilibrium model, we then explore whether reforms along these lines in the actual Dutch tax-benefit system will raise employment without sacrificing equality. The analysis reveals that selective tax relief for elastic secondary earners and low-skilled workers have this potential. A flat income tax structure possibly combined with a negative income tax worsens the equity-efficiency trade-off.

    Constraint-Based Causal Discovery using Partial Ancestral Graphs in the presence of Cycles

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    While feedback loops are known to play important roles in many complex systems, their existence is ignored in a large part of the causal discovery literature, as systems are typically assumed to be acyclic from the outset. When applying causal discovery algorithms designed for the acyclic setting on data generated by a system that involves feedback, one would not expect to obtain correct results. In this work, we show that---surprisingly---the output of the Fast Causal Inference (FCI) algorithm is correct if it is applied to observational data generated by a system that involves feedback. More specifically, we prove that for observational data generated by a simple and σ\sigma-faithful Structural Causal Model (SCM), FCI is sound and complete, and can be used to consistently estimate (i) the presence and absence of causal relations, (ii) the presence and absence of direct causal relations, (iii) the absence of confounders, and (iv) the absence of specific cycles in the causal graph of the SCM. We extend these results to constraint-based causal discovery algorithms that exploit certain forms of background knowledge, including the causally sufficient setting (e.g., the PC algorithm) and the Joint Causal Inference setting (e.g., the FCI-JCI algorithm).Comment: Major revision. To appear in Proceedings of the 36 th Conference on Uncertainty in Artificial Intelligence (UAI), PMLR volume 124, 202

    Markov Properties for Graphical Models with Cycles and Latent Variables

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    We investigate probabilistic graphical models that allow for both cycles and latent variables. For this we introduce directed graphs with hyperedges (HEDGes), generalizing and combining both marginalized directed acyclic graphs (mDAGs) that can model latent (dependent) variables, and directed mixed graphs (DMGs) that can model cycles. We define and analyse several different Markov properties that relate the graphical structure of a HEDG with a probability distribution on a corresponding product space over the set of nodes, for example factorization properties, structural equations properties, ordered/local/global Markov properties, and marginal versions of these. The various Markov properties for HEDGes are in general not equivalent to each other when cycles or hyperedges are present, in contrast with the simpler case of directed acyclic graphical (DAG) models (also known as Bayesian networks). We show how the Markov properties for HEDGes - and thus the corresponding graphical Markov models - are logically related to each other.Comment: 131 page

    Constraint-based Causal Discovery for Non-Linear Structural Causal Models with Cycles and Latent Confounders

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    We address the problem of causal discovery from data, making use of the recently proposed causal modeling framework of modular structural causal models (mSCM) to handle cycles, latent confounders and non-linearities. We introduce {\sigma}-connection graphs ({\sigma}-CG), a new class of mixed graphs (containing undirected, bidirected and directed edges) with additional structure, and extend the concept of {\sigma}-separation, the appropriate generalization of the well-known notion of d-separation in this setting, to apply to {\sigma}-CGs. We prove the closedness of {\sigma}-separation under marginalisation and conditioning and exploit this to implement a test of {\sigma}-separation on a {\sigma}-CG. This then leads us to the first causal discovery algorithm that can handle non-linear functional relations, latent confounders, cyclic causal relationships, and data from different (stochastic) perfect interventions. As a proof of concept, we show on synthetic data how well the algorithm recovers features of the causal graph of modular structural causal models.Comment: Accepted for publication in Conference on Uncertainty in Artificial Intelligence 201
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