docs: def rotate(f,x,theta=0):
      '''
      Returns a function that takes as input the 1D vector along the angle
      given a function that takes in 2D input
      '''
      f_R = lambda b: f(np.array([[x*np.cos(theta)-b*np.sin(theta)],
                                  [x*np.sin(theta)+b*np.cos(theta)]]))
      return f_R