pendulum: better docstring added
pendulum: better docstring added

certik/hermes1d-llnl,certik/hermes1d-llnl,certik/hermes1d,hpfem/hermes1d,certik/hermes1d,hpfem/hermes1d,hpfem/hermes1d,certik/hermes1d,certik/hermes1d-llnl