Returns a function that takes as input the 1D vector along the angle
    given a function that takes in 2D input

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