Conductance of a Markov chain
= Conductance of a Markov chain
{title2=$\Phi(A)$}
For a <reversible Markov chain> with stationary flow $Q(x,y)=\pi(x)P(x,y)$, the conductance of a set $A$ is
$$
\Phi(A)=\frac{Q(A,A^c)}{\pi(A)}.
$$
Its <Cheeger constant> minimizes the boundary flow divided by the smaller stationary mass of the two sides of the cut.