add example

examples/diffusion_2d_mpi_gmg.jl

@@ -0,0 +1,100 @@
+# This file shows how we can use the GeophysicalModelGenerator package to specify an initial model setup
+# it will run on 1 core if you start this from the REPL and on multicores if you run this with:
+# mpiexecjl -n 4 --project=. julia diffusion_2d_mpi_gmg.jl
+# it requires GMG >= 0.7.8
+using Chmy, Chmy.Architectures, Chmy.Grids, Chmy.Fields, Chmy.BoundaryConditions, Chmy.GridOperators, Chmy.KernelLaunch
+using KernelAbstractions
+using Printf
+using CairoMakie
+using GeophysicalModelGenerator
+
+
+# using AMDGPU
+# AMDGPU.allowscalar(false)
+# using CUDA
+# CUDA.allowscalar(false)
+
+using Chmy.Distributed
+using MPI
+MPI.Init()
+
+@kernel inbounds = true function compute_q!(q, C, χ, g::StructuredGrid, O)
+    I = @index(Global, NTuple)
+    I = I + O
+    q.x[I...] = -χ * ∂x(C, g, I...)
+    q.y[I...] = -χ * ∂y(C, g, I...)
+end
+
+@kernel inbounds = true function update_C!(C, q, Δt, g::StructuredGrid, O)
+    I = @index(Global, NTuple)
+    I = I + O
+    C[I...] -= Δt * divg(q, g, I...)
+end
+
+@views function main(backend=CPU(); nxy_l=(126, 126))
+    arch = Arch(backend, MPI.COMM_WORLD, (0, 0))
+    topo = topology(arch)
+    me   = global_rank(topo)
+    # geometry
+    dims_l = nxy_l
+    dims_g = dims_l .* dims(topo)
+    grid   = UniformGrid(arch; origin=(-2, -2), extent=(4, 4), dims=dims_g)
+    launch = Launcher(arch, grid, outer_width=(16, 8))
+
+    #@info "mpi" me grid
+
+    nx, ny = dims_g
+    # physics
+    χ = 1.0
+    # numerics
+    Δt = minimum(spacing(grid))^2 / χ / ndims(grid) / 2.1
+    # allocate fields
+    C = Field(backend, grid, Center())
+    P = Field(backend, grid, Center(), Int32)   # phases
+
+    q = VectorField(backend, grid)
+    C_v = (me==0) ? KernelAbstractions.zeros(CPU(), Float64, size(interior(C)) .* dims(topo)) : nothing
+
+    # use GMG to set the initial conditions
+    add_box!(P,C,grid,  xlim=(-1.0,1.0), zlim=(-1.0,1.0), phase=ConstantPhase(4), T=ConstantTemp(400))
+
+    # set BC's and updates the halo:
+    bc!(arch, grid, C => Neumann(); exchange=C)
+
+    # visualisation
+    fig = Figure(; size=(400, 320))
+    ax  = Axis(fig[1, 1]; aspect=DataAspect(), xlabel="x", ylabel="y", title="it = 0")
+    plt = heatmap!(ax, centers(grid)..., interior(C) |> Array; colormap=:turbo)
+    Colorbar(fig[1, 2], plt)
+    # action
+    nt = 100
+    for it in 1:nt
+        (me==0) && @printf("it = %d/%d \n", it, nt)
+        launch(arch, grid, compute_q! => (q, C, χ, grid))
+        launch(arch, grid, update_C! => (C, q, Δt, grid); bc=batch(grid, C => Neumann(); exchange=C))
+    end
+    KernelAbstractions.synchronize(backend)
+    # local postprocess
+    # plt[3] = interior(C) |> Array
+    # ax.title = "it = $nt"
+    # display(fig)
+    # save("out$me.png", fig)
+    # global postprocess
+    gather!(arch, C_v, C)
+    if me == 0
+        fig = Figure(; size=(400, 320))
+        ax  = Axis(fig[1, 1]; aspect=DataAspect(), xlabel="x", ylabel="y", title="it = 0")
+        plt = heatmap!(ax, C_v; colormap=:turbo) # how to get the global grid for axes?
+        Colorbar(fig[1, 2], plt)
+        save("out_gather_$nx.png", fig)
+    end
+    return
+end
+
+n = 128
+
+# main(ROCBackend(); nxy_l=(n, n) .- 2)
+# main(CUDABackend(); nxy_l=(n, n) .- 2)
+main(; nxy_l=(n, n) .- 2)
+
+MPI.Finalize()