SIRS Markov chain
= SIRS Markov chain
{c}
{title2=$(S,I,R)\to(S-1,I+1,R),\ (S,I-1,R+1),\ (S+1,I,R-1)$}
In a closed population of size $n$, a frequency-dependent SIRS epidemic has the displayed transitions at rates $\lambda SI/n$, $\gamma I$, and $\nu R$. The <exponential distribution> of infectious lifetimes and the constant immunity-loss hazard make the compartment counts a <continuous-time Markov chain>. Each jump preserves $S+I+R=n$.