Which expression describes the divergence of the gradient, ∇⋅(∇f)\nabla \cdot (\nabla f)∇⋅(∇f)?
Hessian HfH_fHf
Laplacian Δf\Delta fΔf
Curl ∇×f\nabla \times f∇×f
Gradient ∇f\nabla f∇f