Paper detail

The one-sided Lipschitz condition in the follow-the-leader approximation of scalar conservation laws

We consider the follow-the-leader particle approximation scheme for a $1d$ scalar conservation law with nonnegative $L^\infty_c$ initial datum and with a $C^1$ concave flux, which is known to provide convergence towards the entropy solution $ρ$ to the corresponding Cauchy problem. We provide two novel contributions to this theory. First, we prove that the one-sided Lipschitz condition satisfied by the approximating density $ρ^n$ is a discrete version of an entropy condition; more precisely, under fairly general assumptions on $f$ (which imply concavity of $f$) we prove that the continuum version $\left(f(ρ)/ρ\right)_x\leq 1/t$ of said condition allows to select a unique weak solution, despite $\left(f(ρ)/ρ\right)_x\leq 1/t$ is apparently weaker than the classical Oleinik-Hoff one-sided Lipschitz condition $f'(ρ)_x\leq 1/t$. Said result relies on an improved version of Hoff's uniqueness proof. A byproduct of it is that the entropy condition is encoded in the particle scheme prior to the many-particle limit, which was never proven before. Second, we prove that in case $f(ρ)=ρ(A-ρ^γ)$ the one-sided Lipschitz condition can be improved to a discrete version of the classical (and sharp) Oleinik-Hoff condition. In order to make the paper self-contained, we provide proofs (in some cases alternative ones) of all steps of the convergence of the particle scheme.