def pendulum_dydt ( t, y ):

#*****************************************************************************80
#
## pendulum_dydt() returns the right hand side of the linear pendulum ODE.
#
  import numpy as np

  g = 9.81
  l = 1.0

  u = y[0]
  v = y[1]

  dudt = v
  dvdt = - ( g / l ) * u

  dydt = np.array ( [ dudt, dvdt ] )

  return dydt