Mass Is Conserved Exactly, Yet the Density Is Negative — The Positivity-Preserving Flux Limiter
·9 min read
At CFL 0.45 a limiter-off double rarefaction dies at step 2: density 0.37, pressure -0.163. One θ per face blends LF and the high-order flux.
Where Negative Density Leaks In — A Positivity-Preserving Flux Limiter for Blast Waves
·6 min read
A Le Blanc rarefaction can drive density negative. Per-face θ blends the high-order flux back toward Lax–Friedrichs only as far as the floor requires.