  The incompressible limit of nonlinear diffusion equations of porous medium
type has attracted a lot of attention in recent years, due to its ability to
link the weak formulation of cell-population models to free boundary problems
of Hele-Shaw type. Although vast literature is available on this singular
limit, little is known on the convergence rate of the solutions. In this work,
we compute the convergence rate in a negative Sobolev norm and, upon
interpolating with BV-uniform bounds, we deduce a convergence rate in
appropriate Lebesgue spaces.
