Field advection

Particles-in-Cell

JustRelax.jl relies on JustPIC.jl for advections of particles containing material information.

The recommended workflow is now:

using JustRelax
using JustPIC, JustPIC._2D

grid = Geometry(ni, li; origin = origin)

nxcell = 24
max_xcell = 36
min_xcell = 12

particles = init_particles(backend, nxcell, max_xcell, min_xcell, grid.xi_vel...)
pT, pPhases = init_cell_arrays(particles, Val(2))
particle_args = (pT, pPhases)
phase_ratios = PhaseRatios(backend, nphases, ni)

grid.xi_vel stores the staggered velocity coordinates used to initialize particles. In most cases you should pass grid.xi_vel... directly to init_particles instead of rebuilding the velocity grids manually from xci, xvi, and di.

Typical particle operations

Common particle operations now follow the compact API used in the tests and examples:

grid2particle!(pT, T_buffer, particles)
particle2grid!(T_buffer, pT, particles)

advection!(particles, RungeKutta2(), @velocity(stokes), dt)
move_particles!(particles, particle_args)
inject_particles_phase!(particles, pPhases, (pT,), (T_buffer,))
update_phase_ratios!(phase_ratios, particles, pPhases)

If you use subgrid diffusion, the matching workflow is:

subgrid_arrays = SubgridDiffusionCellArrays(particles)
dt₀ = similar(stokes.P)

subgrid_characteristic_time!(
    subgrid_arrays, particles, dt₀, phase_ratios, rheology, thermal, stokes
)
centroid2particle!(subgrid_arrays.dt₀, dt₀, particles)
subgrid_diffusion!(pT, T_buffer, thermal.ΔT[2:end-1, :], subgrid_arrays, particles, dt)

Velocity grids

velocity_grids(xci, xvi, di) is still available when you need the staggered coordinates explicitly, for example for analysis or custom utilities. When you already have a Geometry, prefer grid.xi_vel.