def pendulum_conserved ( t, y ):

#*****************************************************************************80
#
## pendulum_conserved() returns a conserved quantity for the pendulum ODE.
#
  u = y[:,0]
  v = y[:,1]

  g = 9.81
  l = 1.0
  m = 1.0

  h = 0.5 * m * g * l * u**2 + 0.5 * m * v**2

  return h