18,792 research outputs found
Solving Set Constraint Satisfaction Problems using ROBDDs
In this paper we present a new approach to modeling finite set domain
constraint problems using Reduced Ordered Binary Decision Diagrams (ROBDDs). We
show that it is possible to construct an efficient set domain propagator which
compactly represents many set domains and set constraints using ROBDDs. We
demonstrate that the ROBDD-based approach provides unprecedented flexibility in
modeling constraint satisfaction problems, leading to performance improvements.
We also show that the ROBDD-based modeling approach can be extended to the
modeling of integer and multiset constraint problems in a straightforward
manner. Since domain propagation is not always practical, we also show how to
incorporate less strict consistency notions into the ROBDD framework, such as
set bounds, cardinality bounds and lexicographic bounds consistency. Finally,
we present experimental results that demonstrate the ROBDD-based solver
performs better than various more conventional constraint solvers on several
standard set constraint problems
Closure statistics in interferometric data
Interferometric visibilities, reflecting the complex correlations between
signals recorded at antennas in an interferometric array, carry information
about the angular structure of a distant source. While unknown antenna gains in
both amplitude and phase can prevent direct interpretation of these
measurements, certain combinations of visibilities called closure phases and
closure amplitudes are independent of antenna gains and provide a convenient
set of robust observables. However, these closure quantities have subtle noise
properties and are generally both linearly and statistically dependent. These
complications have obstructed the proper use of closure quantities in
interferometric analysis, and they have obscured the relationship between
analysis with closure quantities and other analysis techniques such as self
calibration. We review the statistics of closure quantities, noting common
pitfalls that arise when approaching low signal-to-noise due to the nonlinear
propagation of statistical errors. We then develop a strategy for isolating and
fitting to the independent degrees of freedom captured by the closure
quantities through explicit construction of linearly independent sets of
quantities along with their noise covariance in the Gaussian limit, valid for
moderate signal-to-noise, and we demonstrate that model fits have biased
posteriors when this covariance is ignored. Finally, we introduce a unified
procedure for fitting to both closure information and partially calibrated
visibilities, and we demonstrate both analytically and numerically the direct
equivalence of inference based on closure quantities to that based on self
calibration of complex visibilities with unconstrained antenna gains.Comment: 31 pages, 17 figure
Reducing Redundancies in Reconfigurable Antenna Structures Using Graph Models
We present an approach for reducing redundancies in the design of reconfigurable antenna structures using graph models. The basics of graph models, their rules, and how they can be applied in the design of switch-based reconfigurable antennas are introduced. Based on these rules, a methodology is developed and formulated to reduce the number of switches and parts in the antenna structure, without sacrificing the desired antenna functions. This approach not only optimizes the overall structure of the antenna but it also reduces cost and overall losses. Several examples are presented and discussed to demonstrate the validity of this new approach through simulations and measurements that present good agreement
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