function duvdt = pendulum_deriv ( t, uv )

%*****************************************************************************80
%
%% pendulum_deriv returns the derivative for the pendulum ODE.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    20 February 2020
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    real T(:), UV(2), the arguments of the derivative.
%
%  Output:
%
%    real DUVDT(2,1), the value of the derivative.
%
  g = 9.8;
  l = 1.0;

  u = uv(1);
  v = uv(2);

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

  duvdt = [ dudt; dvdt ];

  return
end

