text: """
  =========================
  Integrating a simple ODE
  =========================
  
  Solve the ODE dy/dt = -2y between t = 0..4, with the initial condition
  y(t=0) = 1.
  """
  
  import numpy as np
  from scipy.integrate import odeint
  from matplotlib import pyplot as plt
  
  def calc_derivative(ypos, time):
      return -2*ypos
  
  time_vec = np.linspace(0, 4, 40)
  yvec = odeint(calc_derivative, 1, time_vec)
  
  plt.figure(figsize=(4, 3))
  plt.plot(time_vec, yvec)
  plt.xlabel('t: Time')
  plt.ylabel('y: Position')
  plt.tight_layout()
  
  