Degree six returned 9 where 15 was required — the three Hermite roots that fixed D2Q9
·8 min read
Where c_s² = 1/3 and the weights 4/9, 1/9, 1/36 actually come from, traced all the way back to the degree of a Gauss–Hermite quadrature rule.
Surviving the Low-Viscosity Regime Where BGK Blows Up — MRT Lattice Boltzmann Collision
·5 min read
At nu=0.004 the shear rate s_nu is 1.953. BGK copies that rate onto every ghost mode; the MRT rates in the listing keep s_e at 1.64 and s_q at 1.7.
Nine Arrows of Maxwell–Boltzmann — Why LBM's Equilibrium Is a Polynomial
·7 min read
Cutting Maxwell–Boltzmann at Hermite order two builds the D2Q9 polynomial, and that same cut leaves the Mach 0.3 ceiling in place.