import numpy as np
f = lambda x, y: np.sin(2 * x + 2 * y)
fx = lambda x, y: np.cos(f(x, y))
fy = lambda x, y: np.sin(f(x, y))
plot_vector([fx, fy], ("x", -1, 1), ("y", -1, 1),
    streamlines=True, scalar=False, use_cm=False)  # doctest: +SKIP