plot_vector(v, (x, -3, 3), (y, -3, 3),
    streamlines=True, scalar=None,
    stream_kw={"density": 1.5},
    label="Magnitude of %s" % str(v), xlabel="x", ylabel="y")
# Expected:
## Plot object containing:
## [0]: 2D vector series: [sin(x - y), cos(x + y)] over (x, -3.0, 3.0), (y, -3.0, 3.0)