Working with CellArrays

Instantiating a CellArray

With the help of ParallelStencil.jl we can easily create a CellArray object. The CellArray object is a container that holds the data of a grid. The data is stored in small nD-arrays, and the grid is divided into cells. Each cell contains a number of elements. The CellArray object is used to store the data of the particles in the simulation.

using JustPIC, JustPIC._2D
using ParallelStencil
@init_parallel_stencil(Threads, Float64, 2)

julia> ni = (2, 2)
(2, 2)

julia> ncells = (2,)
(2,)

julia> x = 20
20

julia> CA = @fill(x, ni..., celldims = ncells, eltype = Float64) 
2×2 CellArrays.CPUCellArray{StaticArraysCore.SVector{2, Float64}, 2, 1, Float64}:
 [20.0, 20.0]  [20.0, 20.0]
 [20.0, 20.0]  [20.0, 20.0]

Indexing a CellArray

We can access to the data of one CellArray by indexing a given grid cell. This will however instantiate a StaticArray object with the data of the cell.

julia> CA[1,1]
2-element StaticArraysCore.SVector{2, Float64} with indices SOneTo(2):
 20.0
 20.0

It is however useful to read and mutate the data of the CellArray object directly, without instantiating a StaticArray. For this porpuse, JustPIC exports the macro @index to directly read and mutate the individual elements of the cell.

For example, to read a single element of CA:

julia> @index CA[2, 1, 1]
20.0

where, in this case, the first index corresponds to the 2nd element of the data within $cell_{11}$ cell. We can mutate the CellArray in a similar way:

julia> @index CA[2, 1, 1] = 0.0
0.0

julia> CA
2×2 CellArrays.CPUCellArray{StaticArraysCore.SVector{2, Float64}, 2, 1, Float64}:
 [20.0, 0.0]   [20.0, 20.0]
 [20.0, 20.0]  [20.0, 20.0]

JustPIC also provides the macro @cell operatig at the cell level:

julia> @cell CA[1,1]
2-element StaticArraysCore.SVector{2, Float64} with indices SOneTo(2):
 20.0
 20.0

julia> @cell CA[1,1] = @cell(CA[1,1]) .+ 1
2-element StaticArraysCore.SVector{2, Float64} with indices SOneTo(2):
 21.0
 21.0

 julia> CA
2×2 CellArrays.CPUCellArray{StaticArraysCore.SVector{2, Float64}, 2, 1, Float64}:
 [21.0, 21.0]  [20.0, 20.0]
 [20.0, 20.0]  [20.0, 20.0]