Burgers Riemann problem with negative flux
= Burgers Riemann problem with negative flux
{c}
{title2=$F(f)=-f^2/2$}
For left state zero and right state $U$, negative-flux <Inviscid Burgers equation> gives a shock at $\theta=-UZ/2$ when $U>0$, and a <rarefaction wave> $f=-\theta/Z$ on $0<\theta<-UZ$ when $U<0$. This is the standard positive-flux equation after setting $u=-f$; <entropy solution> selection reverses which step direction is compressive.