For example, the motion generated by P can be found by solving the Heisenberg equation of motion using P as a Hamiltonian, d X = i [ X , P ] d s = d s d P = i [ P , P ] d s = 0 . These are translations of the matrix X by a multiple of the identity matrix, X → → X + s I . This is the interpretation of the derivative operator D : e = e, the exponential of a derivative operator is a translation (so Lagrange's shift operator).