4 research outputs found
Mass fluctuation kinetics: analysis and computation of equilibria and local dynamics
The mass fluctuation kinetics (MFK) model is a set of coupled ordinary differential equations approximating the time evolution of means and covariances of species concentrations in chemical reaction networks. It generalises classical mass action kinetics (MAK), in which fluctuations around the mean are ignored. MFK may be used to approximate stochasticity in system trajectories when stochastic simulation methods are prohibitively expensive computationally. This study presents a set of tools to aid in the analysis of systems within the MFK framework. A closed-form expression for the MFK Jacobian matrix is derived. This expression facilitates the computation of MFK equilibria and the characterisation of the dynamics of small deviations from the equilibria (i.e. local dynamics). Software developed in MATLAB to analyse systems within the MFK framework is also presented. The authors outline a homotopy continuation method that employs the Jacobian for bifurcation analysis, that is, to generate a locus of steady-state Jacobian eigenvalues corresponding to changing a chosen MFK parameter such as system volume or a rate constant. This method is applied to study the effect of small-volume stochasticity on local dynamics at equilibria in a pair of example systems, namely the formation and dissociation of an enzyme-substrate complex and a genetic oscillator. For both systems, this study reveals volume regimes where MFK provides a quantitatively and/or qualitatively correct description of system behaviour, and regimes where the MFK approximation is inaccurate. Moreover, our analysis provides evidence that decreasing volume from the MAK regime (infinite volume) has a destabilising effect on system dynamics
Probabilistic Model Checking for Continuous-Time Markov Chains via Sequential Bayesian Inference
Probabilistic model checking for systems with large or unbounded state space
is a challenging computational problem in formal modelling and its
applications. Numerical algorithms require an explicit representation of the
state space, while statistical approaches require a large number of samples to
estimate the desired properties with high confidence. Here, we show how model
checking of time-bounded path properties can be recast exactly as a Bayesian
inference problem. In this novel formulation the problem can be efficiently
approximated using techniques from machine learning. Our approach is inspired
by a recent result in statistical physics which derived closed form
differential equations for the first-passage time distribution of stochastic
processes. We show on a number of non-trivial case studies that our method
achieves both high accuracy and significant computational gains compared to
statistical model checking