def test_fd_derivative():
x = B.linspace(0, 10, 50)
y = np.sin(x)
p = GP(0.7 * EQ().stretch(1.0))
dp = (p.shift(-1e-3) - p.shift(1e-3)) / 2e-3
post = p.measure | (p(x), y)
approx(post(dp)(x).mean, np.cos(x)[:, None], atol=1e-4)
def test_shifting():
# Test construction:
p = GP(lambda x: x**2, Linear())
assert str(p.shift(1)) == "GP(<lambda> shift 1, Linear() shift 1)"
# Test case:
p_shifted = p.shift(5)
x = B.linspace(0, 5, 10)
y = p_shifted(x).sample()
post = p.measure | (p_shifted(x, B.epsilon), y)
assert_equal_normals(post(p(x - 5)), post(p_shifted(x)))
assert_equal_normals(post(p(x)), post(p_shifted(x + 5)))
