code: def skew_matrix(w):
      '''Return the skew matrix of a direction w.'''
      return np.array([[0, -w[2], w[1]],
                       [w[2], 0, -w[0]],
                       [-w[1], w[0], 0]]f skew_matrix(w):
      '''Return the skew matrix of a direction w.'''
      return np.array([[0, -w[2], w[1]],
                       [w[2], 0, -w[0]],
                       [-w[1], w[0], 0]])
docs: Return the skew matrix of a direction w.