Pointer Programs and Undirected Reachability

Pointer programs are a model of structured computation within logspace. They capture the common description of logspace algorithms as programs that take as input some structured data (e.g. a graph) and that store in memory only a constant number of pointers to the input (e.g. to the graph nodes). In this paper we study undirected s-t-reachability for a class of pure pointer programs in which one can work with a constant number of abstract pointers, but not with arbitrary data, such as memory registers of logarithmic size. In earlier work we have formalised this class as a programming language purple that features a forallloop for iterating over the input structure and thus subsumes other formalisations of pure pointer programs, such as Jumping Automata on Graphs ( jags) and Deterministic Transitive Closure logic ( dtc-logic) for locally ordered graphs. In this paper we show that purple cannot decide undirected s-t-reachability, even though there does exist a logspace-algorithm for thi...

• Type: Conference
• Year: 2009
• Where: LICS
• Authors: Martin Hofmann, Ulrich Schöpp
• Keywords: Computer Science, LICS 2009, Pointer Programs, Pure Pointer Programs, Undirected S-t-reachability