Heat map in Julia - julia

Question

I am a new user and have no idea how to solve this error:
using AbstractGPs
using LinearAlgebra
using Plots
using Random
using PlutoUI
randomseed=42
Random.seed!(randomseed)
X = rand(datapoints) .* 2 .- 1
PES(x)=x^2
plot(-1:0.01:1, PES, label="Underlying potential", xlabel="Position", ylabel="Energy")
Y = PES.(X)
kernelfunction=SEKernel()
Xrange=range(-3,3; length=100)
plot(heatmap(kernelmatrix(kernelfunction, Xrange); yflip=true))
Stack trace:
MethodError: no method matching Val{:heatmap}(::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char, ::Char)
1. apply_recipe(::Dict{Symbol,Any}, ::Type{Val{:heatmap}}, ::Plots.Plot{Plots.GRBackend})#recipes.jl:49
2. _process_plotrecipe(::Any, ::Any, ::Any, ::Any)#plot_recipe.jl:32
3. _process_plotrecipes!(::Any, ::Any)#plot_recipe.jl:18
4. recipe_pipeline!(::Any, ::Any, ::Any)#RecipesPipeline.jl:81
5. _plot!(::Plots.Plot, ::Any, ::Any)#plot.jl:208
6. #plot#154#plot.jl:91[inlined]
7. #heatmap#406(::Any, ::typeof(Plots.heatmap), ::Any)#RecipesBase.jl:404
8. top-level scope#Local: 2[inlined]

Answer 1

Not sure what you did wrong but this
using AbstractGPs, LinearAlgebra, Plots, Random # removed PlutoUI
randomseed = 42
Random.seed!(randomseed)
datapoints = 100 # Added for code to be self-contained
X = rand(datapoints) .* 2 .- 1
PES(r) = r^2
# removed first plot
Y = PES.(X)
kernelfunction = SEKernel()
Xrange = range(-3, 3; length=100)
heatmap(kernelmatrix(kernelfunction, Xrange); yflip=true) # removed unnecessary call to `plot`
gives me