Transitive closure algorithm MEMTC and its performance analysis

AbstractIn this paper, we present a new algorithm for computing the full transitive closure designed for operation in layered memories. The algorithm is based on strongly connected component detection and on a very compact representation of data. We analyze the average-case performance of the algorithm experimentally in an environment where two layers of memory of different speed are used. In our analysis, we use trace-based simulation of memory operations

Stop It, and Be Stubborn!

A system is AG EF terminating, if and only if from every reachable state, a terminal state is reachable. This publication argues that it is beneficial for both catching non-progress errors and stubborn set state space reduction to try to make verification models AG EF terminating. An incorrect mutual exclusion algorithm is used as an example. The error does not manifest itself, unless the first action of the customers is modelled differently from other actions. An appropriate method is to add an alternative first action that models the customer stopping for good. This method typically makes the model AG EF terminating. If the model is AG EF terminating, then the basic strong stubborn set method preserves safety and some progress properties without any additional condition for solving the ignoring problem. Furthermore, whether the model is AG EF terminating can be checked efficiently from the reduced state space

Symbolic Lookaheads for Bottom-up Parsing

We present algorithms for the construction of LALR(1) parsing tables, and of LR(1) parsing tables of reduced size. We first define specialized characteristic automata whose states are parametric w.r.t. variables symbolically representing lookahead-sets. The propagation flow of lookaheads is kept in the form of a system of recursive equations, which is resolved to obtain the concrete LALR(1) table. By inspection of the LALR(1) automaton and of its lookahead ropagation flow, we decide whether the grammar is LR(1) or not. In the positive case, an LR(1) parsing table of reduced size is computed by refinement of the LALR(1) table