def test_truncated_gaussian_entropy(mu=0.0, sigma=1.0):
"""
Consider
Z ~ N(mu,1)
versus
A ~ Bern(p) for p = 1-Phi(-mu)
Z ~ A * TN(mu, 1, 0, Inf) + (1-A) * TN(mu, 1, -Inf, 0)
We have simply separated the Gaussian sampling into two steps:
1. Sample the sign of Z
2. Sample Z from a truncated normal.
Thus, E_Z[LN p(Z)] should equal E_A[ E_{Z|A} [LN p (Z | A)]]
using iterated expectations.
:return:
"""
p = 1.0 - normal_cdf(0, mu, sigma)
print "p: ", p
# Compute the entropy of the scalar Gaussian
H0 = ScalarGaussian(mu=mu, sigmasq=sigma**2).negentropy()
# Compute the entropy of the two stage process
# H1 = p * TruncatedScalarGaussian(lb=0, mu=mu, sigmasq=sigma).negentropy() + \
# (1-p) * TruncatedScalarGaussian(ub=0, mu=mu, sigmasq=sigma).negentropy()
TN1 = TruncatedScalarGaussian(lb=0, mu=mu, sigmasq=sigma)
EZ1 = TN1.expected_x()
EZ1sq = TN1.expected_xsq()
H1 = p * ScalarGaussian(mu=mu, sigmasq=sigma).negentropy(E_x=EZ1,
E_xsq=EZ1sq)
TN0 = TruncatedScalarGaussian(ub=0, mu=mu, sigmasq=sigma)
EZ0 = TN0.expected_x()
EZ0sq = TN0.expected_xsq()
H1 += (1 - p) * ScalarGaussian(mu=mu, sigmasq=sigma).negentropy(
E_x=EZ0, E_xsq=EZ0sq)
H2 = -norm(loc=mu, scale=sigma).entropy()
# H3 = -p * truncnorm((0-mu)/sigma, np.inf, loc=mu).entropy() + \
# -(1-p) * truncnorm(-np.inf, (0-mu)/sigma, loc=mu).entropy()
print "H0: ", H0
print "H1: ", H1
print "H2: ", H2
def test_truncated_scalar_gaussian_lb():
tn0_test = TruncatedScalarGaussian(lb=0)
tn0_true = truncnorm(0, np.Inf)
print "E[TN(0,inf)]:\t", tn0_test.expected_x()
print "E[TN(0,inf)]:\t", tn0_true.mean()
assert np.allclose(tn0_test.expected_x(), tn0_true.mean())
print "Var[TN(0,inf)]:\t", tn0_test.variance_x()
def test_truncated_scalar_gaussian():
lb = 0
ub = 10
mu = 3
sigma = 1
tn0_test = TruncatedScalarGaussian(mu=mu,
sigmasq=np.sqrt(sigma),
lb=lb,
ub=ub)
tn0_true = truncnorm((lb - mu) / sigma, (ub - mu) / sigma, loc=mu)
print "E[TN(0,10)]:\t", tn0_test.expected_x()
print "E[TN(0,10)]:\t", tn0_true.mean()
assert np.allclose(tn0_test.expected_x(), tn0_true.mean())
print "Var[TN(0,10)]:\t", tn0_test.variance_x()
print "Var[TN(0,10)]:\t", tn0_true.var()
assert np.allclose(tn0_test.variance_x(), tn0_true.var())
print "E[-LN{TN(0,10)}]:\t", -tn0_test.negentropy()
print "E[-LN{TN(0,10)}]:\t", tn0_true.entropy()
assert np.allclose(-tn0_test.negentropy(), tn0_true.entropy())
