It is shown that, by applying an "accelerated" or "multi-step" ladder-operatorial procedure, one can obtain, easily, a symmetric closed-form expression for the off-diagonal ($n\ne n^{\prime },l\ne l^{\prime }$) hydrogenic $r^k$ matrix elements.

• Received 9 July 1973

DOI:https://doi.org/10.1103/PhysRevA.8.2246