On Dirichlet eigenvectors for neutral two-dimensional Markov chains

Nicolas Champagnat (1, 2) , Persi Diaconis (3) , Laurent Miclo (4)

1 IECN - Institut Élie Cartan de Nancy
2 TOSCA - TO Simulate and CAlibrate stochastic models
3 Department of Statistics [Stanford]
4 IMT - Institut de Mathématiques de Toulouse UMR5219

We consider a general class of discrete, two-dimensional Markov chains modeling the dynamics of a population with two types, without mutation or immigration, and neutral in the sense that type has no influence on each individual's birth or death parameters. We prove that all the eigenvectors of the corresponding transition matrix or infinitesimal generator \Pi\ can be expressed as the product of "universal" polynomials of two variables, depending on each type's size but not on the specific transitions of the dynamics, and functions depending only on the total population size. These eigenvectors appear to be Dirichlet eigenvectors for \Pi\ on the complement of triangular subdomains, and as a consequence the corresponding eigenvalues are ordered in a specific way. As an application, we study the quasistationary behavior of finite, nearly neutral, two-dimensional Markov chains, absorbed in the sense that 0 is an absorbing state for each component of the process.

Mots clés: coexistence; Yaglom limit; Dirichlet eigenvalue; quasi-stationary distribution; Hahn polynomials; two-dimensional difference equation; neutral Markov chain; multitype population dynamics; Dirichlet eigenvector

Domaines: Probabilités [math.PR]

Nicolas Champagnat, Persi Diaconis, Laurent Miclo. On Dirichlet eigenvectors for neutral two-dimensional Markov chains. Electronic Journal of Probability, 2012, 17 (63), pp.1-41. ⟨10.1214/EJP.v17-1830⟩. ⟨hal-00672938⟩