Using an array comprehension works for me, i.e.,
function ddp_diversity(X::AbstractArray)
D = ndims(X)
@assert D == 3
n_samples = size(X,D)
K = [1/(1 + norm(selectdim(X,D,i) .- selectdim(X,D,j)))
for i ∈ 1:n_samples, j ∈ 1:n_samples]
return det(K)
end
Find that more readable anyways …