Alow plotting kernel without nodeset (#31)

* allow plotting kernel without nodeset

* format

src/visualization.jl

@@ -1,3 +1,22 @@
+@recipe function f(kernel::AbstractKernel{Dim}; x_min = -1.0, x_max = 1.0,
+                   N = 50) where {Dim}
+    if Dim == 1
+        x = LinRange(x_min, x_max, N)
+        title --> get_name(kernel)
+        x, kernel.(Ref(0.0), x)
+    elseif Dim == 2
+        nodeset = homogeneous_hypercube(N, x_min, x_max; dim = 2)
+        x = unique(values_along_dim(nodeset, 1))
+        y = unique(values_along_dim(nodeset, 2))
+        z = reshape(kernel.(Ref([0.0, 0.0]), nodeset), (N, N))
+        seriestype --> :heatmap # :contourf
+        title --> get_name(kernel)
+        x, y, z
+    else
+        @error("Plotting a kernel is only supported for dimension up to 2, but the kernel has dimension $Dim")
+    end
+end
+
 @recipe function f(x::AbstractVector, kernel::AbstractKernel)
     xguide --> "r"
     title --> get_name(kernel)
@@ -14,6 +33,7 @@ end
         y = values_along_dim(nodeset, 2)
         seriestype --> :scatter
         label --> "nodes"
+        title --> get_name(kernel)
         x, y, kernel.(Ref([0.0, 0.0]), nodeset)
     else
         @error("Plotting a kernel is only supported for dimension up to 2, but the set has dimension $(dim(nodeset))")

test/test_unit.jl

@@ -571,14 +571,17 @@ using Plots
     @testset "Visualization" begin
         f = sum
         kernel = GaussKernel{3}(shape_parameter = 0.5)
+        kernel_1d = Matern12Kernel{1}()
         trafo_kernel = TransformationKernel{2}(kernel, x -> [x[1] + x[2]^2, x[1]])
         @test_nowarn plot(-1.0:0.1:1.0, kernel)
         for dim in 1:3
             nodes = homogeneous_hypercube(5; dim = dim)
             @test_nowarn plot(nodes)
             if dim < 3
                 @test_nowarn plot(nodes, kernel)
-                # Transformtion kernel can only be plotted in the dimension of the input of the trafo
+                @test_nowarn plot(kernel_1d)
+                @test_nowarn plot(trafo_kernel, x_min = -2, x_max = 2, N = 100)
+                # Transformation kernel can only be plotted in the dimension of the input of the trafo
                 if dim == 2
                     @test_nowarn plot(nodes, trafo_kernel)
                 end