Let us specialize to the expectation value of the energy for one particle in three-dimensions. This expectation value reads E=∫dxdydzψ∗(x,y,z)ˆHψ(x,y,z), with the constraint ∫dxdydzψ∗(x,y,z)ψ(x,y,z)=1, and a Hamiltonian ˆH=−12∇2+V(x,y,z). We will, for the sake of notational convenience, skip the variables x,y,z below, and write for example V(x,y,z)=V.