Add helper function bounding_box

CHANGELOG.md

@@ -262,6 +262,10 @@ more discussion).
 
 - VTK export now work with `QuadraticHexahedron` elements. ([#714][github-714])
 
+- The function `bounding_box(::AbstractGrid)` has been added. It computes the bounding box for 
+  a given grid (based on its node coordinates), and returns the minimum and maximum vertices 
+  of the bounding box. ([#880][github-880])
+
 ### Changed
 
 - `create_sparsity_pattern` now supports cross-element dof coupling by passing kwarg
@@ -891,3 +895,5 @@ poking into Ferrite internals:
 [github-779]: https://github.com/Ferrite-FEM/Ferrite.jl/pull/779
 [github-835]: https://github.com/Ferrite-FEM/Ferrite.jl/pull/835
 [github-855]: https://github.com/Ferrite-FEM/Ferrite.jl/pull/855
+[github-880]: https://github.com/Ferrite-FEM/Ferrite.jl/pull/880
+

src/Grid/utils.jl

@@ -340,3 +340,25 @@ for (func,                   entity_f,            entity_t,     filter_f,
     end
 end
 end
+
+
+
+"""
+    bounding_box(grid::AbstractGrid)
+
+Computes the axis-aligned bounding box for a given grid, based on its node coordinates. 
+Returns the minimum and maximum vertex coordinates of the bounding box.
+"""
+function bounding_box(grid::AbstractGrid{dim}) where {dim}
+    T = get_coordinate_eltype(grid)
+    min_vertex = Vec{dim}(i->typemax(T))
+    max_vertex = Vec{dim}(i->typemin(T))
+    for node in getnodes(grid)
+        x = get_node_coordinate(node)
+        _max_tmp = max_vertex # avoid type instability
+        _min_tmp = min_vertex
+        max_vertex = Vec{dim}(i -> max(x[i], _max_tmp[i]))
+        min_vertex = Vec{dim}(i -> min(x[i], _min_tmp[i]))
+    end
+    return min_vertex, max_vertex
+end

test/test_abstractgrid.jl

@@ -82,6 +82,10 @@
     @test Ferrite.ndofs(dhs[1]) == Ferrite.ndofs(dhs[2])
     @test isapprox(u1,u2,atol=1e-8)
 
+    minv, maxv = Ferrite.bounding_box(subtype_grid)
+    @test minv ≈ Vec((-1.0,-1.0))
+    @test maxv ≈ Vec((+1.0,+1.0))
+
     colors1 = Ferrite.create_coloring(subtype_grid, alg = ColoringAlgorithm.WorkStream)
     colors2 = Ferrite.create_coloring(reference_grid, alg = ColoringAlgorithm.WorkStream)
     @test all(colors1 .== colors2)

test/test_grid_dofhandler_vtk.jl

@@ -91,6 +91,10 @@ end
             rm(dofhandlerfilename*".vtu")
         end
 
+        minv, maxv = Ferrite.bounding_box(grid)
+        @test minv ≈ 2left
+        @test maxv ≈ 2right
+
     end
 
 end # of testset