Memory Efficient Data Structures for Explicit Verification of Timed Systems

Abstract. Timed analysis of real-time systems can be performed us-ing continuous (symbolic) or discrete (explicit) techniques. The explicit state-space exploration can be considerably faster for models with mod-erately small constants, however, at the expense of high memory con-sumption. In the setting of timed-arc Petri nets, we explore new data structures for lowering the used memory: PTries for efficient storing of configurations and time darts for semi-symbolic description of the state-space. Both methods are implemented as a part of the tool TAPAAL and the experiments document at least one order of magnitude of memory savings while preserving comparable verification times.

The octahedron abstract domain

Abstract. An interesting area in static analysis is the study of numeric properties. Complex properties can be analyzed using abstract interpretation, provided that an adequate abstract domain is defined. Each domain can represent and manipulate a family of properties, providing a different trade-off between the precision and complexity of the analysis. The contribution of this paper is a new numeric abstract domain called octahedron that represents constraints of the form (±xj ±... ± xk ≥ c), where xi are numerical variables such that xi ≥ 0. The implementation of octahedra is based on a new kind of decision diagrams called Octahedron Decision Diagrams (OhDD).

Experimental characterization of the Xe 5p photoionization by angle- and spin-resolved photoelectron spectroscopy

Heckenkamp C, Schäfers F, Schönhense G, Heinzmann U. Experimental characterization of the Xe 5p photoionization by angle- and spin-resolved photoelectron spectroscopy. Zeitschrift für Physik D: Atoms, Molecules and Clusters. 1986;2(4):257-274.Spin- and angle-resolved photoelectron spectroscopy with elliptically polarized radiation has been used to fully characterize the dynamics of photoelectron emission from free Xe atoms in the 5p-autoionization and continuum region. An advantageous reaction geometry and its experimental realization at the storage ring BESSY are discussed. The three independent experimental parameters which characterize the angular dependence of the photoelectron spin-polarization vector are reported for the wavelength range from 100nm to 40 nm. The results are compared with theoretical predictions based on RRPA-, RPAE- and semiempirical MQDT-calculations. The combination of existing data for the differential photoionization cross section with the spinpolarization parameters is used to completely decouple the photoionization channels: The transition matrix elements and their relative phases are determined separately for every single dissociation channel. The results are discussed in the context of the MQDT. Correlation effects and the influence of spin-orbit interaction on the continuum states most clearly show up when the Dill-Fano angular-momentum-transfer formalism is applied

Can Decision Diagrams Overcome State Space Explosion in Real-Time Verification?

In this paper we analyze the efficiency of binary decision diagrams (BDDs) and clock difference diagrams (CDDs) in the verification of timed automata. Therefore we present analytical and empirical complexity results for three communication protocols. The contributions of the analyses are: Firstly, they show that BDDs and CDDs of polynomial size exist for the reachability sets of the three protocols. This is the first evidence that CDDs can grow only polynomially for models with non-trivial state space explosion. Secondly, they show that CDD-based tools, which currently use at least exponential space for two of the protocols, will only find polynomial-size CDDs if they use better variable orders, as the BDD-based tool Rabbit does. Finally, they give insight into the dependency of the BDD and CDD size on properties of the model, in particular the number of automata and the magnitude of the clock values