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#Numerical-Analysis

~44 min read

Pushing the cell Péclet number to 2 drove the solution to -0.33 — where the energy to minimize disappeared

·7 min read

Advection breaks the symmetry of the stiffness matrix, and the minimum total potential energy principle goes with it. Here is the real cause of Galerkin oscillations and what stabilization buys instead.

I Dropped the −1/2 and the Viscosity Came Back Six Times Too Large — the Δt/2 Left Behind by LBM's Discretisation

·6 min read

One trapezoidal integration and one change of variables leave a Δt/2 in three separate places: the viscosity, the velocity, and the stress. A scalar ODE and a D2Q9 lattice measure all three.

What Jacobi Cannot Kill in 10,000 Sweeps, a V-Cycle Kills in 10 — The Real Secret of Multigrid

·6 min read

Swap the grid, swap the frequency: how a hierarchy converts stubborn low modes into easy ones

Implicit Diffusion and the Thomas Algorithm — Buying Stability with One Tridiagonal Solve

·4 min read

Past the explicit blow-up wall, the cost of unconditional stability is one O(N) sweep

When Characteristics Collide, a Shock Is Born — Burgers and the (x,t) Plane

·5 min read

How nonlinear self-advection breaks a smooth curve into a shock.

Quadtree AMR — Letting the Mesh Grow Where It Needs To

·6 min read

Forty years of adaptive mesh data structures and refinement criteria, since Berger–Oliger

When Lax–Wendroff Shook at a Step — Building a 2nd-Order TVD Advection Scheme with Flux Limiters

·5 min read

Sidestep Godunov's theorem to build a monotone 2nd-order advection scheme

Choosing a CFD Linear Solver: Comparing Convergence Speeds from Jacobi to BiCGSTAB

·5 min read

Comparing the characteristics and convergence speeds of the four major Krylov subspace solvers with code and simulation.