45,843 research outputs found
A Scalable MCEM Estimator for Spatio-Temporal Autoregressive Models
Very large spatio-temporal lattice data are becoming increasingly common
across a variety of disciplines. However, estimating interdependence across
space and time in large areal datasets remains challenging, as existing
approaches are often (i) not scalable, (ii) designed for conditionally Gaussian
outcome data, or (iii) are limited to cross-sectional and univariate outcomes.
This paper proposes an MCEM estimation strategy for a family of latent-Gaussian
multivariate spatio-temporal models that addresses these issues. The proposed
estimator is applicable to a wide range of non-Gaussian outcomes, and
implementations for binary and count outcomes are discussed explicitly. The
methodology is illustrated on simulated data, as well as on weekly data of
IS-related events in Syrian districts.Comment: 29 pages, 8 figure
Full QCD with the L\"uscher local bosonic action
We investigate L\"uscher's method of including dynamical Wilson fermions in a
lattice simulation of QCD with two quark flavours. We measure the accuracy of
the approximation by comparing it with Hybrid Monte Carlo results for gauge
plaquette and Wilson loops. We also introduce an additional global Metropolis
step in the update. We show that the complexity of L\"uscher's algorithm
compares favourably with that of the Hybrid Monte Carlo.Comment: 21 pages Late
Determinants and Perfect Matchings
We give a combinatorial interpretation of the determinant of a matrix as a
generating function over Brauer diagrams in two different but related ways. The
sign of a permutation associated to its number of inversions in the Leibniz
formula for the determinant is replaced by the number of crossings in the
Brauer diagram. This interpretation naturally explains why the determinant of
an even antisymmetric matrix is the square of a Pfaffian.Comment: 15 pages, terminology improved, exposition tightened, "deranged
matchings" example remove
Counting eigenvalues in domains of the complex field
A procedure for counting the number of eigenvalues of a matrix in a region
surrounded by a closed curve is presented. It is based on the application of
the residual theorem. The quadrature is performed by evaluating the principal
argument of the logarithm of a function. A strategy is proposed for selecting a
path length that insures that the same branch of the logarithm is followed
during the integration. Numerical tests are reported for matrices obtained from
conventional matrix test sets.Comment: 21 page
Data optimizations for constraint automata
Constraint automata (CA) constitute a coordination model based on finite
automata on infinite words. Originally introduced for modeling of coordinators,
an interesting new application of CAs is implementing coordinators (i.e.,
compiling CAs into executable code). Such an approach guarantees
correctness-by-construction and can even yield code that outperforms
hand-crafted code. The extent to which these two potential advantages
materialize depends on the smartness of CA-compilers and the existence of
proofs of their correctness.
Every transition in a CA is labeled by a "data constraint" that specifies an
atomic data-flow between coordinated processes as a first-order formula. At
run-time, compiler-generated code must handle data constraints as efficiently
as possible. In this paper, we present, and prove the correctness of two
optimization techniques for CA-compilers related to handling of data
constraints: a reduction to eliminate redundant variables and a translation
from (declarative) data constraints to (imperative) data commands expressed in
a small sequential language. Through experiments, we show that these
optimization techniques can have a positive impact on performance of generated
executable code
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