Pierluigi Frisco

Simulating Counter Automata by P Systems with Symport/Antiport

The complexity, expressed in number of membranes and weight of rules, of P systems with symport/antiport generating recursively enumerable sets is reduced if counter automata instead of matrix grammars are simulated. We consider both subsets of N obtained by counting objects in a designated membrane, and string languages obtained by following the traces of a designated object.

The conformon-P system: a molecular and cell biology-inspired computability model

A new theoretical computational model, called conformon-P system, based on simple and basic concepts inspired from a theoretical model of the living cell and membrane computing is presented.The computational power of it and of some natural variants are studied.Links with Petri nets, reversible computation, other interpretations and variants of the model are briefly outlined.

Dynamics of HIV infection studied with cellular automata and conformon-P systems

Recently a cellular automaton (CA) has been used to model the dynamics of HIV infection, with interesting results. We replicate and further test this model, and we introduce an alternative model based on conformon-P (cP) systems. We find (in common with other recently published comments) that the CA model is very sensitive to initial conditions and produces appropriate qualitative dynamics only for a narrow range of rule probabilities. In contrast, the cP system model is robust to a wide range of conditions and parameters, with more reproducible qualitative agreement to the overall dynamics and to the densities of healthy and infected cells observed in vivo.

About P systems with symport/antiport

It is proved that four membranes suffice to a variant of P systems with symport/antiport with maximal parallelism to generate all recursively enumerable sets of numbers. P systems with symport/antiport without maximal parallelism are also studied, considering two termination criteria.

P systems, petri nets, and program machines

Some features capturing the computational completeness of P systems with maximal parallelism, priorities or zero-test using symbol objects are studied through Petri nets. The obtained results are not limited to P systems.

P systems with symport/antiport simulating counter automata

Abstract.The generative capability of several variants of P systems with symport/antiport is studied via the simulation of counter automata. This leads to the reduction of the complexity, expressed in number of membranes and weight of rules, of P systems generating recursively enumerable sets.

On Stateless Multihead Finite Automata and Multihead Pushdown Automata

A stateless k-head two-way deterministic finite automaton (k-head 2DFA), has only one state, hence the designation stateless. Its transitions depends solely on the symbols currently scanned by its k heads, and in every such transition each head can move one cell left, right, or remain stationary. An input, which is delimited by end markers, is accepted if the machine, when started with all heads on the left end marker, reaches the configuration where all the heads are on the right end marker. The nondeterministic version is denoted by k-head 2NFA. We prove that stateless (k + 1)-head 2DFAs (resp., 2NFAs) are computationally more powerful than k-head 2DFAs (resp., 2NFAs), improving a recent result where it was shown that (k + 4) heads are better than k heads. We also study stateless multihead pushdown automata in their two-way and one-way, deterministic and nondeterministic variations and show that for all these varieties, k + 1 heads allow more computational power than k heads. Finally, we give some characterizations of stateless multihead finite and multihead pushdown automata.

Towards a Hierarchy of Conformons-P Systems

The combination of a theoretical model of the living cell and membrane computing suggested a new variant of a computational model called conformons-P system based on membrane-enclosed compartments where conformon-like objects evolve. Some variants of such model are presented and their computational power is sketched.

Computing by only observing

The paradigm of evolution/observation is based on the idea that a computing device can be obtained by combining a basic system and an observer that transforms the evolution of the basic system into a readable output. In this framework we investigate what can be computed by changing the observer but not the basic observed system. We consider grammars as basic systems combined with finite state automata as observers, watching either the sequence of sentential forms or the productions used by the grammar. It is possible to obtain computational completeness only varying the observer, without modifying the basic system, which is a fixed context-free grammar.

A simulator and an evolution program for conformon-P systems

A simulator for conformon-P systems is presented together with an initial study of an evolution program optimising processes described by conformon-P systems.