Abstract. We consider a stochastic process driven by a linear ordinary differential equation whose right-hand side switches at exponential times between a collection of different matrices. We construct planar examples that switch between two matrices where the individual matrices and the average of the two matrices are all Hurwitz (all eigenvalues have strictly negative real part), but nonetheless the process goes to infinity at large time for certain values of the switching rate. We further construct examples in higher dimensions where again the two individual matrices and their averages are all Hurwitz, but the process has arbitrarily many transitions between going to zero and going to infinity at large time as the switching rate varies. In order to construct these examples, we first prove in general that if each of the individual matrices is Hurwitz, then the process goes to zero at large time for sufficiently slow switching rate and if the average matrix is Hurwitz, then the process goes to zero at large time for sufficiently fast switching rate. We also give simple conditions that ensure the process goes to zero at large time for all switching rates.Key words. Ergodicity, piecewise deterministic Markov process, switched dynamical systems, hybrid switching system, planar switched systems, linear differential equations.AMS subject classifications. 60J75, 93E15, 37H15, 34F05, 34D23.
IntroductionWe consider the stochastic process (X t ) t≥0 ∈ R d where X t solvesẊ t = A It X t with I t a Markov process on a finite set E and {A i } i∈E a set of d × d real matrices. The stability of this system when the switching process I t is deterministic has been extensively studied in the past decade; see [2] and [12].In [6], the authors study the stochastic problem in the plane with I t a Markov process and E = {0,1}. The authors assume both A 0 and A 1 are Hurwitz (all eigenvalues have strictly negative real part) and prove the surprising result that ||X t || may converge to 0 or +∞ as t → ∞ depending on the switching rate as long as an average matrixĀ = λA 0 + (1 − λ)A 1 has a positive eigenvalue for some λ ∈ (0,1).In this paper, we show that the assumption that the average matrix has a positive eigenvalue is not necessary to ensure a blowup. Specifically, we construct examples in the plane where A 0 , A 1 , andĀ = λA 0 + (1 − λ)A 1 are all Hurwitz, but ||X t || → +∞ almost surely as t → ∞ for certain values of the switching rate. This is significant for the general study of switching processes because it shows that the dynamics of the switching process can be very different from both the individual dynamics (in this case, the A i 's) and the averaged dynamics (in this case,Ā). These planar examples are also interesting because they have multiple transitions between ||X t || going to 0 and going to +∞ at large time as the switching rate varies. Furthermore, we construct examples in higher dimensions that have arbitrarily many such phase transitions.Recently researchers have devoted considerable attention to randomly switc...