Laplace-Runge-Lenz vector (source code)

= Laplace-Runge-Lenz vector
{c}
{title2=$\mathbf A$}
{wiki=Laplace–Runge–Lenz_vector}

For the repulsive inverse-square Hamiltonian $H=\mathbf p^2/(2m)+k/r$, the Laplace-Runge-Lenz vector
$$
\mathbf A=\mathbf p\times\mathbf L+mk\widehat{\mathbf r}
$$
is conserved. It obeys $\mathbf A\cdot\mathbf L=0$ and $A^2=m^2k^2+2mHL^2$.