laplace_diffusion_entropy_variables_3d.jl

function LaplaceDiffusionEntropyVariables3D(diffusivity, equations_hyperbolic)
    LaplaceDiffusionEntropyVariables{3, typeof(equations_hyperbolic),
                                     nvariables(equations_hyperbolic),
                                     typeof(diffusivity)}(diffusivity, equations_hyperbolic)
end

function flux(u, gradients, orientation::Integer,
              equations::LaplaceDiffusionEntropyVariables{3})
    dudx, dudy, dudz = gradients
    diffusivity = jacobian_entropy2cons(u, equations)
    if orientation == 1
        return SVector(diffusivity * dudx)
    elseif orientation == 2
        return SVector(diffusivity * dudy)
    else # if orientation == 3
        return SVector(diffusivity * dudz)
    end
end