pub fn parallel_count_particles(
positions: &[[f64; 3]],
n_cells: [usize; 3],
cell_size: f64,
) -> Vec<usize>Expand description
Count how many particles fall into each cell of a regular grid.
The grid has n_cells = [nx, ny, nz] cells, each of side length cell_size.
The origin is [0, 0, 0]. Particles outside the grid are clamped to the
nearest boundary cell.
Returns a flat Vec of length nx * ny * nz.