function dxyzdt = arneodo_deriv ( t, xyz )

%*****************************************************************************80
%
%% arneodo_deriv() evaluates the right hand side of arneodo_ode().
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    16 September 2021
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Alain Arneodo, Pierre Coullet, Edward Spiegel, Charles Tresser,
%    Asymptotic Chaos,
%    Physica D: Nonlinear Phenomena,
%    Volume 14, Number 3, 1985, pages 327-347.
%
%    Stephen Lucas, Evelyn Sander, Laura Taalman,
%    Modeling dynamical systems for 3D printing,
%    Notices of the American Mathematical Society,
%    Volume 67, Number 11, December 2020, pages 1692-1705.
%
%  Input:
%
%    real t: the value of the independent variable.
%
%    real xyz: the values of the dependent variables at time T.
%
%  Output:
%
%    real dxyzdt: the right hand side of the ODE.
%
  [ alpha, beta, delta, t0, xyz0, tstop ] = arneodo_parameters ( );

  x = xyz(1);
  y = xyz(2);
  z = xyz(3);

  dxdt = y;
  dydt = z;
  dzdt = - alpha * x - beta * y - z + delta * x^3;

  dxyzdt = [ dxdt; dydt; dzdt ];

  return
end

