  A nonnegative coarse Ricci curvature for a Markov chain and the existence of
an attractive point implies the concentration of the invariant probability
measure around this point. The mass outside balls centered at the attractive
point, as a function of the radius, decreases at least as fast as the
exponential of a double integral of the coarse Ricci curvature. This is exactly
the behaviour of the density of the reversible measure for diffusion processes
on the real line.
