new_contents: import matplotlib.pyplot as plt
  import numpy as np
  
  T = 2
  mu = 0.1
  sigma = 0.01
  S0 = 20
  dt = 0.01
  N = round(T/dt)
  t = np.linspace(0, T, N)
  W = np.random.standard_normal(size = N) 
  W = np.cumsum(W)*np.sqrt(dt) ### standard brownian motion ###
  X = (mu-0.5*sigma**2)*t + sigma*W 
  S = S0*np.exp(X) ### geometric brownian motion ###
  plt.plot(t, S)
  plt.show()
  
subject: Create GBM_simulation.py