383 research outputs found
Limited bisimulations for nondeterministic fuzzy transition systems
The limited version of bisimulation, called limited approximate bisimulation,
has recently been introduced to fuzzy transition systems (NFTSs). This article
extends limited approximate bisimulation to NFTSs, which are more general
structures than FTSs, to introduce a notion of -limited
-bisimulation by using an approach of relational lifting, where is
a natural number and . To give the algorithmic
characterization, a fixed point characterization of -limited
-bisimilarity is first provided. Then -limited -bisimulation
vector with -th element being a -limited -bisimulation is
introduced to investigate conditions for two states to be -limited
-bisimilar, where . Using these results, an
O(2k^2|V|^6\cdot\left|\lra\right|^2) algorithm is designed for computing the
degree of similarity between two states, where is the number of states of
the NFTS and \left|\lra\right| is the greatest number of transitions from
states. Finally, the relationship between -limited -bisimilar and
-bisimulation under is showed, and by which, a logical
characterization of -limited -bisimilarity is provided
Minimization of Dynamical Systems over Monoids
Quantitative notions of bisimulation are well-known tools for the
minimization of dynamical models such as Markov chains and ordinary
differential equations (ODEs). In \emph{forward bisimulations}, each state in
the quotient model represents an equivalence class and the dynamical evolution
gives the overall sum of its members in the original model. Here we introduce
generalized forward bisimulation (GFB) for dynamical systems over commutative
monoids and develop a partition refinement algorithm to compute the coarsest
one. When the monoid is , we recover %our framework recovers
probabilistic bisimulation for Markov chains and more recent forward
bisimulations for %systems of nonlinear ODEs. %ordinary differential equations.
Using we get %When the monoid is we
can obtain nonlinear reductions for discrete-time dynamical systems and ODEs
%ordinary differential equations where each variable in the quotient model
represents the product of original variables in the equivalence class. When the
domain is a finite set such as the Booleans , we can apply GFB to
Boolean networks (BN), a widely used dynamical model in computational biology.
Using a prototype implementation of our minimization algorithm for GFB, we find
disjunction- and conjunction-preserving reductions on 60 BN from two well-known
repositories, and demonstrate the obtained analysis speed-ups. We also provide
the biological interpretation of the reduction obtained for two selected BN,
and we show how GFB enables the analysis of a large one that could not be
analyzed otherwise. Using a randomized version of our algorithm we find
product-preserving (therefore non-linear) reductions on 21 dynamical weighted
networks from the literature that could not be handled by the exact algorithm.Comment: Accepted at Thirty-Eighth Annual ACM/IEEE Symposium on Logic in
Computer Science (LICS), 202
Probabilistic Bisimulations for PCTL Model Checking of Interval MDPs
Verification of PCTL properties of MDPs with convex uncertainties has been
investigated recently by Puggelli et al. However, model checking algorithms
typically suffer from state space explosion. In this paper, we address
probabilistic bisimulation to reduce the size of such an MDPs while preserving
PCTL properties it satisfies. We discuss different interpretations of
uncertainty in the models which are studied in the literature and that result
in two different definitions of bisimulations. We give algorithms to compute
the quotients of these bisimulations in time polynomial in the size of the
model and exponential in the uncertain branching. Finally, we show by a case
study that large models in practice can have small branching and that a
substantial state space reduction can be achieved by our approach.Comment: In Proceedings SynCoP 2014, arXiv:1403.784
Efficient Local Computation of Differential Bisimulations via Coupling and Up-to Methods
We introduce polynomial couplings, a generalization of probabilistic couplings, to develop an algorithm for the computation of equivalence relations which can be interpreted as a lifting of probabilistic bisimulation to polynomial differential equations, a ubiquitous model of dynamical systems across science and engineering. The algorithm enjoys polynomial time complexity and complements classical partition-refinement approaches because: (a) it implements a local exploration of the system, possibly yielding equivalences that do not necessarily involve the inspection of the whole system of differential equations; (b) it can be enhanced by up-to techniques; and (c) it allows the specification of pairs which ought not be included in the output. Using a prototype, these advantages are demonstrated on case studies from systems biology for applications to model reduction and comparison. Notably, we report four orders of magnitude smaller runtimes than partition-refinement approaches when disproving equivalences between Markov chains
Probabilistic Guarded KAT Modulo Bisimilarity: Completeness and Complexity
We introduce Probabilistic Guarded Kleene Algebra with Tests (ProbGKAT), an extension of GKAT that allows reasoning about uninterpreted imperative programs with probabilistic branching. We give its operational semantics in terms of special class of probabilistic automata. We give a sound and complete Salomaa-style axiomatisation of bisimilarity of ProbGKAT expressions. Finally, we show that bisimilarity of ProbGKAT expressions can be decided in O(n3 log n) time via a generic partition refinement algorithm
Modelling MAC-Layer Communications in Wireless Systems
We present a timed process calculus for modelling wireless networks in which
individual stations broadcast and receive messages; moreover the broadcasts are
subject to collisions. Based on a reduction semantics for the calculus we
define a contextual equivalence to compare the external behaviour of such
wireless networks. Further, we construct an extensional LTS (labelled
transition system) which models the activities of stations that can be directly
observed by the external environment. Standard bisimulations in this LTS
provide a sound proof method for proving systems contextually equivalence. We
illustrate the usefulness of the proof methodology by a series of examples.
Finally we show that this proof method is also complete, for a large class of
systems
- âŠ