scalar_expr = sqrt((-sin(y))**2 + cos(x)**2)
graphics(
    vector_field_2d(-sin(y), cos(x), (x, -5, 5), (y, -3, 3), n=20,
        scalar=[scalar_expr, "$%s$" % latex(scalar_expr)],
        contour_kw={"cmap": "summer"},
        quiver_kw={"color": "k"}),
    vector_field_2d(2 * y, x, (x, -5, 5), (y, -3, 3), n=20,
        scalar=False, quiver_kw={"color": "r"}, use_cm=False),
    aspect="equal", grid=False, xlabel="x", ylabel="y")
# Expected:
## Plot object containing:
## [0]: contour: sqrt(sin(y)**2 + cos(x)**2) for x over (-5.0, 5.0) and y over (-3.0, 3.0)
## [1]: 2D vector series: [-sin(y), cos(x)] over (x, -5.0, 5.0), (y, -3.0, 3.0)
## [2]: 2D vector series: [2*y, x] over (x, -5.0, 5.0), (y, -3.0, 3.0)