Radu Nicolescu

Parallel and distributed algorithms in p systems

Our groups recent quest has been to use P systems to model parallel and distributed algorithms. Several framework extensions are recalled or detailed, in particular, modular composition with information hiding, complex symbols, generic rules, reified cell IDs, asynchronous operational modes, asynchronous complexity. We motivate our proposals via P system models of several well-known distributed algorithms, such as leader election and distributed echo. As another type of application, we mention a dynamic programming algorithm for stereo matching in image processing. We suggest criteria to assess the merits of this modelling approach and offer preliminary evaluations of our proposed additional ingredients, which have been useful in refactoring existing systems and could be useful to the larger P systems community.

P Systems and the Byzantine Agreement

Abstract We first propose a modular framework for recursive composition of P systems. This modular approach provides encapsulation and information hiding, facilitating the design of P programs for complex algorithms. Using this framework, we developed a P program that solves the classical version of the Byzantine agreement problem, for N participants connected in a complete graph, according to the well known Byzantine agreement algorithm based on EIG trees. We prove the correctness of this modular composition and conclude with a list of open problems.

Edge- and Node-Disjoint Paths in P Systems

In this paper, we continue our development of algorithms used for topological network discovery. We present native P system versions of two fundamental problems in graph theory: finding the maximum number of edge- and node-disjoint paths between a source node and target node. We start from the standard depth-first-search maximum flow algorithms, but our approach is totally distributed, when initially no structural information is available and each P system cell has to even learn its immediate neighbors. For the node-disjoint version, our P system rules are designed to enforce node weight capacities (of one), in addition to edge capacities (of one), which are not readily available in the standard network flow algorithms.

Asynchronous P Systems

In this paper, the authors propose a new approach to fully asynchronous P systems, and a matching complexity measure, both inspired from the field of distributed algorithms. The authors validate the proposed approach by implementing several well-known distributed depth-first search (DFS) and breadth-first search (BFS) algorithms. Empirical results show that the proposed P algorithms have shorter descriptions and achieve a performance comparable to the corresponding distributed algorithms.

BFS solution for disjoint paths in P systems

This paper continues the research on determining a maximum cardinality set of edge- and node-disjoint paths between a source cell and a target cell in P systems. With reference to the previously proposed solution [3], based on depth-first search (DFS), we propose a faster solution, based on breadth-first search (BFS), which leverages the parallel and distributed characteristics of P systems. The runtime complexity shows that, our BFS-based solution performs better than the DFS-based solution, in terms of P steps.

P systems in stereo matching

Designing parallel versions of sequential algorithms has attracted renewed attention, due to recent hardware advances, including various general-purpose multi-core, multiple core and many-core processors, as well as special-purpose FPGA implementations. P systems consist of networks of autonomous cells, such that each cell transforms its input signals in accord with symbol-rewriting rules and feeds the output results into its immediate neighbours. Inherent intra- and inter-cell parallelism make the P systems a prospective theoretical testbed for designing parallel algorithms. This paper discusses capabilities of P systems to implement the symmetric dynamic programming algorithm for stereo matching, with due account to binocular or monocular visibility of 3D surface points.

Discovering the membrane topology of hyperdag p systems

In an earlier paper, we presented an extension to the families of P systems, called hyperdag P systems (hP systems), by proposing a new underlying topological structure based on the hierarchical dag structure (instead of trees or digraphs). In this paper, we develop building-block membrane algorithms for discovery of the global topological structure from the local cell point of view. In doing so, we propose more convenient operational modes and transfer modes, that depend only on each of the individual cell rules. Finally, by extending our initial work on the visualization of hP system membranes with interconnections based on dag structures without transitive arcs, we propose several ways to represent structural relationships, that may include transitive arcs, by simple-closed planar regions, which are folded (and possibly twisted) in three dimensional space.

An environment for automated performance evaluation of J2EE and ASP.NET thin-client architectures

Assessing the likely run-time performance of applications using thin-client architectures during their design is very difficult. We describe SoftArch/Thin, a thin-client test-bed generator that synthesises performance test-bed thin-client and server code from high-level software architecture models. This generated code is performance tested using a third-party tool and the results summarised. Architecture models can be evolved and tests repeated during application development to inform software engineers of realistic performance characteristics of their designs. Our environment currently supports J2EE and ASP.NET-based thin-client code generation and performance testing.

Advance in vision-based driver assistance

Vision-based driver assistance is an active safety measure currently under development in various car companies and research institutes worldwide. The paper informs about related activities at The University of Auckland, focussing on stereo vision, performance evaluation, provided test data, and currently developed components.

New Solutions to the Firing Squad Synchronization Problems for Neural and Hyperdag P Systems

We propose two uniform solutions to an open question: the Firing Squad Synchronization Problem (FSSP), for hyperdag and symmetric neural P systems, with anonymous cells. Our solutions take e_c+5 and 6e_c+7 steps, respectively, where e_c is the eccentricity of the commander cell of the dag or digraph underlying these P systems. The first and fast solution is based on a novel proposal, which dynamically extends P systems with mobile channels. The second solution is substantially longer, but is solely based on classical rules and static channels. In contrast to the previous solutions, which work for tree-based P systems, our solutions synchronize to any subset of the underlying digraph; and do not require membrane polarizations or conditional rules, but require states, as typically used in hyperdag and neural P systems.