def METHOD_NAME():
    # singel 2d coordinate transformation
    center_x, center_y = 0, 0
    x = 1
    y = 1
    r, phi = param_util.cart2polar(x, y, center_x, center_y)
    assert r == np.sqrt(2)  # radial part
    assert phi == np.arctan(1)
    # array of 2d coordinates
    x = np.array([1, 2])
    y = np.array([1, 1])
    r, phi = param_util.cart2polar(x, y, center_x, center_y)
    assert r[0] == np.sqrt(2)  # radial part
    assert phi[0] == np.arctan(1)