Congruent Weak Conformance

This research addresses the problem of verifying implementations against specifications through an innovative logic approach. Congruent weak conformance, a formal relationship between agents and specifications, has been developed and proven to be a congruent partial order. This property arises from a set of relations called weak conformations. The largest, called weak conformance, is analogous to Milner\u27s observational equivalence. Weak conformance is not an equivalence, however, but rather an ordering relation among processes. Weak conformance allows behaviors in the implementation that are unreachable in the specification. Furthermore, it exploits output concurrencies and allows interleaving of extraneous output actions in the implementation. Finally, reasonable restrictions in CCS syntax strengthen weak conformance to a congruence, called congruent weak conformance. At present, congruent weak conformance is the best known formal relation for verifying implementations against specifications. This precongruence derives maximal flexibility and embodies all weaknesses in input, output, and no-connect signals while retaining a fully replaceable conformance to the specification. Congruent weak conformance has additional utility in verifying transformations between systems of incompatible semantics. This dissertation describes a hypothetical translator from the informal simulation semantics of VHDL to the bisimulation semantics of CCS. A second translator is described from VHDL to a broadcast-communication version of CCS. By showing that they preserve congruent weak conformance, both translators are verified

Congruent weak conformance

Journal ArticleCongruent weak conformance is a property between formal models capturing the desired relationship between a specification and its implementation by allowing unused and redundant circuitry and tolerating unspec4jied behavior in the unreachable state space. By providing greater flexibility in design than previous properties, U becomes a useful tool to validate transformational systems, such as logic synthesis and hardware description language translation systems

Numerical Study of a Field Theory for Directed Percolation

A numerical method is devised for study of stochastic partial differential equations describing directed percolation, the contact process, and other models with a continuous transition to an absorbing state. Owing to the heightened sensitivity to fluctuationsattending multiplicative noise in the vicinity of an absorbing state, a useful method requires discretization of the field variable as well as of space and time. When applied to the field theory for directed percolation in 1+1 dimensions, the method yields critical exponents which compare well against accepted values.Comment: 18 pages, LaTeX, 6 figures available upon request LC-CM-94-00

Congruent Weak Conformance

Abstract—Congruent weak conformance is a property between formal models capturing the desired relationship between a specification and its implementation by allowing unused and redundant circuitry and tolerating unspecified behavior in the unreachable state space. By providing greater flexibility in design than previous properties, it becomes a useful tool to validate transformational systems, such as logic synthesis and hardware description language translation systems. Index terms—formal methods, process algebras, congruence, conformance, hardware equivalence. I

Relative value of clinical variables, bicycle ergometry, rest radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring at discharge to predict 1 year survival after myocardial infarction

The relative value of predischarge clinical variables, bicycle ergometry, radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring for predicting survival during the first year in 351 hospital survivors of acute myocardial infarction was assessed. Discriminant function analysis showed that in patients eligible for stress testing the extent of blood pressure increase during exercise slightly improved the predictive accuracy beyond that of simple clinical variables (history of previous myocardial infarction, persistent heart failure after the acute phase of infarction and use of digitalis at discharge), whereas radionuclide ventriculography and 24 hour electrocardiographic monitoring did not. The predictive value for mortality was 12% with clinical variables alone and 15% with the stress test added.Radionuclide ventriculography and 24 hour electrocardiographic monitoring were slightly additive to clinical information in the whole group of patients independent of the eligibility for stress testing (predictive value for mortality 24% with clinical variables alone and 26% with radionuclide ejection fraction and 24 hour electrocardiographic monitoring added).It is concluded that the appropriate use of simple clinical variables and stress testing is sufficient for risk stratification in postinfarction patients, whereas radionuclide ventriculography and 24 hour electrocardiographic monitoring should be limited to patients not eligible for stress testing