3,203 research outputs found
Learning a Static Analyzer from Data
To be practically useful, modern static analyzers must precisely model the
effect of both, statements in the programming language as well as frameworks
used by the program under analysis. While important, manually addressing these
challenges is difficult for at least two reasons: (i) the effects on the
overall analysis can be non-trivial, and (ii) as the size and complexity of
modern libraries increase, so is the number of cases the analysis must handle.
In this paper we present a new, automated approach for creating static
analyzers: instead of manually providing the various inference rules of the
analyzer, the key idea is to learn these rules from a dataset of programs. Our
method consists of two ingredients: (i) a synthesis algorithm capable of
learning a candidate analyzer from a given dataset, and (ii) a counter-example
guided learning procedure which generates new programs beyond those in the
initial dataset, critical for discovering corner cases and ensuring the learned
analysis generalizes to unseen programs.
We implemented and instantiated our approach to the task of learning
JavaScript static analysis rules for a subset of points-to analysis and for
allocation sites analysis. These are challenging yet important problems that
have received significant research attention. We show that our approach is
effective: our system automatically discovered practical and useful inference
rules for many cases that are tricky to manually identify and are missed by
state-of-the-art, manually tuned analyzers
Neutron scattering in a d_{x^2-y^2}-wave superconductor with strong impurity scattering and Coulomb correlations
We calculate the spin susceptibility at and below T_c for a d_{x^2-y^2}-wave
superconductor with resonant impurity scattering and Coulomb correlations. Both
the impurity scattering and the Coulomb correlations act to maintain peaks in
the spin susceptibility, as a function of momentum, at the Brillouin zone edge.
These peaks would otherwise be suppressed by the superconducting gap. The
predicted amount of suppression of the spin susceptibility in the
superconducting state compared to the normal state is in qualitative agreement
with results from recent magnetic neutron scattering experiments on
La_{1.86}Sr_{0.14}CuO_4 for momentum values at the zone edge and along the zone
diagonal. The predicted peak widths in the superconducting state, however, are
narrower than those in the normal state, a narrowing which has not been
observed experimentally.Comment: 24 pages (12 tarred-compressed-uuencoded Postscript figures), REVTeX
3.0 with epsf macros, UCSBTH-94-1
Protecting backaction-evading measurements from parametric instability
Noiseless measurement of a single quadrature in systems of parametrically
coupled oscillators is theoretically possible by pumping at the sum and
difference frequencies of the two oscillators, realizing a backaction-evading
(BAE) scheme. Although this would hold true in the simplest scenario for a
system with pure three-wave mixing, implementations of this scheme are hindered
by unwanted higher-order parametric processes that destabilize the system and
add noise. We show analytically that detuning the two pumps from the sum and
difference frequencies can stabilize the system and fully recover the BAE
performance, enabling operation at otherwise inaccessible cooperativities. We
also show that the acceleration demonstrated in a weak signal detection
experiment [PRX QUANTUM 4, 020302 (2023)] was only achievable because of this
detuning technique.Comment: 7 pages, 3 figure
Inducing safer oblique trees without costs
Decision tree induction has been widely studied and applied. In safety applications, such as determining whether a chemical process is safe or whether a person has a medical condition, the cost of misclassification in one of the classes is significantly higher than in the other class. Several authors have tackled this problem by developing cost-sensitive decision tree learning algorithms or have suggested ways of changing the
distribution of training examples to bias the decision tree learning process so as to take account of costs. A prerequisite for applying such algorithms is the availability of costs of misclassification.
Although this may be possible for some applications, obtaining reasonable estimates of costs of misclassification is not easy in the area of safety.
This paper presents a new algorithm for applications where the cost of misclassifications cannot be quantified, although the cost of misclassification in one class is known to be significantly higher than in another class. The algorithm utilizes linear discriminant analysis to identify oblique relationships between continuous attributes and then carries out an appropriate modification to ensure that the resulting tree errs on the side of safety. The algorithm is evaluated with respect to one of the best known cost-sensitive algorithms (ICET), a well-known oblique decision tree algorithm (OC1) and an algorithm that utilizes robust linear programming
An intelligent assistant for exploratory data analysis
In this paper we present an account of the main features of SNOUT, an intelligent assistant for exploratory data analysis (EDA) of social science survey data that incorporates a range of data mining techniques. EDA has much in common with existing data mining techniques: its main objective is to help an investigator reach an understanding of the important relationships ina data set rather than simply develop predictive models for selectd variables. Brief descriptions of a number of novel techniques developed for use in SNOUT are presented. These include heuristic variable level inference and classification, automatic category formation, the use of similarity trees to identify groups of related variables, interactive decision tree construction and model selection using a genetic algorithm
A survey of cost-sensitive decision tree induction algorithms
The past decade has seen a significant interest on the problem of inducing decision trees that take account of costs of misclassification and costs of acquiring the features used for decision making. This survey identifies over 50 algorithms including approaches that are direct adaptations of accuracy based methods, use genetic algorithms, use anytime methods and utilize boosting and bagging. The survey brings together these different studies and novel approaches to cost-sensitive decision tree learning, provides a useful taxonomy, a historical timeline of how the field has developed and should provide a useful reference point for future research in this field
Infrared conductivity of a d_{x^2-y^2}-wave superconductor with impurity and spin-fluctuation scattering
Calculations are presented of the in-plane far-infrared conductivity of a
d_{x^2-y^2}-wave superconductor, incorporating elastic scattering due to
impurities and inelastic scattering due to spin fluctuations. The impurity
scattering is modeled by short-range potential scattering with arbitrary phase
shift, while scattering due to spin fluctuations is calculated within a
weak-coupling Hubbard model picture. The conductivity is characterized by a
low-temperature residual Drude feature whose height and weight are controlled
by impurity scattering, as well as a broad peak centered at 4 Delta_0 arising
from clean-limit inelastic processes. Results are in qualitative agreement with
experiment despite missing spectral weight at high energies.Comment: 29 pages (11 tar-compressed-uuencoded Postscript figures), REVTeX 3.0
with epsf macro
Theory of Thermal Conductivity in YBa_2Cu_3O_{7-\delta}
We calculate the electronic thermal conductivity in a d-wave superconductor,
including both the effect of impurity scattering and inelastic scattering by
antiferromagnetic spin fluctuations. We analyze existing experiments,
particularly with regard to the question of the relative importance of
electronic and phononic contributions to the heat current, and to the influence
of disorder on low-temperature properties. We find that phonons dominate heat
transport near T_c, but that electrons are responsible for most of the peak
observed in clean samples, in agreement with a recent analysis of Krishana et
al. In agreement with recent data on YBa_2(Cu_1-xZn_x)_3O_7-\delta the peak
position is found to vary nonmonotonically with disorder.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
Quasiparticle-quasiparticle Scattering in High Tc Superconductors
The quasiparticle lifetime and the related transport relaxation times are the
fundamental quantities which must be known in order to obtain a description of
the transport properties of the high T_c superconductors. Studies of these
quantities have been undertaken previously for the d-wave, high T_c
superconductors for the case of temperature-independent elastic impurity
scattering. However, much less is known about the temperature-dependent
inelastic scattering. Here we give a detailed description of the
characteristics of the temperature-dependent quasiparticle-quasiparticle
scattering in d-wave superconductors, and find that this process gives a
natural explanation of the rapid variation with temperature of the electrical
transport relaxation rate.Comment: 4 page
Method for Measuring the Momentum-Dependent Relative Phase of the Superconducting Gap of High-Temperature Superconductors
The phase variation of the superconducting gap over the (normal) Fermi
surface of the high-temperature superconductors remains a significant
unresolved question. Is the phase of the gap constant, does it change sign, or
is it perhaps complex? A detailed answer to this question would provide
important constraints on various pairing mechanisms. Here we propose a new
method for measuring the relative gap PHASE on the Fermi surface which is
direct, is angle-resolved, and probes the bulk. The required experiments
involve measuring phonon linewidths in the normal and superconducting state,
with resolution available in current facilities. We primarily address the
La_1.85Sr_.15CuO_4 material, but also propose a more detailed study of a
specific phonon in Bi_2Sr_2CaCu_2O_8.Comment: 13 pages (revtex) + 5 figures (postscript-included), NSF-ITP-93-2
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