def test_compute_mi_cc():
# For two continuous variables a good approach is to test on bivariate
# normal distribution, where mutual information is known.
# Mean of the distribution, irrelevant for mutual information.
mean = np.zeros(2)
# Setup covariance matrix with correlation coeff. equal 0.5.
sigma_1 = 1
sigma_2 = 10
corr = 0.5
cov = np.array([
[sigma_1**2, corr * sigma_1 * sigma_2],
[corr * sigma_1 * sigma_2, sigma_2**2]
])
# True theoretical mutual information.
I_theory = (np.log(sigma_1) + np.log(sigma_2) -
0.5 * np.log(np.linalg.det(cov)))
rng = check_random_state(0)
Z = rng.multivariate_normal(mean, cov, size=1000)
x, y = Z[:, 0], Z[:, 1]
# Theory and computed values won't be very close, assert that the
# first figures after decimal point match.
for n_neighbors in [3, 5, 7]:
I_computed = _compute_mi(x, y, False, False, n_neighbors)
assert_almost_equal(I_computed, I_theory, 1)
def test_compute_mi_cd():
# To test define a joint distribution as follows:
# p(x, y) = p(x) p(y | x)
# X ~ Bernoulli(p)
# (Y | x = 0) ~ Uniform(-1, 1)
# (Y | x = 1) ~ Uniform(0, 2)
# Use the following formula for mutual information:
# I(X; Y) = H(Y) - H(Y | X)
# Two entropies can be computed by hand:
# H(Y) = -(1-p)/2 * ln((1-p)/2) - p/2*log(p/2) - 1/2*log(1/2)
# H(Y | X) = ln(2)
# Now we need to implement sampling from out distribution, which is
# done easily using conditional distribution logic.
n_samples = 1000
rng = check_random_state(0)
for p in [0.3, 0.5, 0.7]:
x = rng.uniform(size=n_samples) > p
y = np.empty(n_samples)
mask = x == 0
y[mask] = rng.uniform(-1, 1, size=np.sum(mask))
y[~mask] = rng.uniform(0, 2, size=np.sum(~mask))
I_theory = -0.5 * ((1 - p) * np.log(0.5 * (1 - p)) +
p * np.log(0.5 * p) + np.log(0.5)) - np.log(2)
# Assert the same tolerance.
for n_neighbors in [3, 5, 7]:
I_computed = _compute_mi(x, y, True, False, n_neighbors)
assert_almost_equal(I_computed, I_theory, 1)
def test_compute_mi_cd_unique_label():
# Test that adding unique label doesn't change MI.
n_samples = 100
x = np.random.uniform(size=n_samples) > 0.5
y = np.empty(n_samples)
mask = x == 0
y[mask] = np.random.uniform(-1, 1, size=np.sum(mask))
y[~mask] = np.random.uniform(0, 2, size=np.sum(~mask))
mi_1 = _compute_mi(x, y, True, False)
x = np.hstack((x, 2))
y = np.hstack((y, 10))
mi_2 = _compute_mi(x, y, True, False)
assert_equal(mi_1, mi_2)
def test_compute_mi_dd():
# In discrete case computations are straightforward and can be done
# by hand on given vectors.
x = np.array([0, 1, 1, 0, 0])
y = np.array([1, 0, 0, 0, 1])
H_x = H_y = -(3/5) * np.log(3/5) - (2/5) * np.log(2/5)
H_xy = -1/5 * np.log(1/5) - 2/5 * np.log(2/5) - 2/5 * np.log(2/5)
I_xy = H_x + H_y - H_xy
assert_almost_equal(_compute_mi(x, y, True, True), I_xy)
