Exponential relaxation time
= Exponential relaxation time
{title2=$u(t)-u_\infty=[u(0)-u_\infty]e^{-t/\tau}$}
For a stable first-order linear equation $u'=-(u-u_\infty)/\tau$, the time $\tau>0$ is the interval over which a deviation from equilibrium decays by the factor $e^{-1}$. This is the dynamical exponential-decay sense, distinct from a Markov chain's spectral relaxation time.