Particle-In-Cell (PIC) is a technique commonly used to simulate motion of charged particles, or plasma.
plasma（等离子体）: a gas of ions and atoms
Basic Physics: Coulomb force（库仑力）, Lorentz force（洛伦兹力）
Motivation: we could simulate plasma by computing the storm of particles directly, but plasma simulations generally require at least 1M particles to reduce numerical errors (n²-problem - not feasible), especially when a typical simulation requires Ks of steps
PIC: Compute an electric field from the particles and then compute forces from the electric field (size-n problem). Group a large number of real particles into one computational particle (let ratio be “specific weight”, a.k.a.
$\nabla$ (nabla operator - generates one of gradient $\nabla f$, divergence $\nabla\cdot f$ or curl $\nabla\times f$)
Fundamental equations: See below