def m2(self):
"""matrix: Second moment."""
if self._m2 is None:
self._m2 = B.cholsolve(B.chol(self.prec),
self.prec + B.outer(self.lam))
self._m2 = B.cholsolve(B.chol(self.prec), B.transpose(self._m2))
return self._m2
def kl(self, other: "NaturalNormal"):
"""Compute the Kullback-Leibler divergence with respect to another normal
parametrised by its natural parameters.
Args:
other (:class:`.NaturalNormal`): Other.
Returns:
scalar: KL divergence with respect to `other`.
"""
ratio = B.solve(B.chol(self.prec), B.chol(other.prec))
diff = self.mean - other.mean
return 0.5 * (B.sum(ratio**2) - B.logdet(B.mm(
ratio, ratio, tr_a=True)) + B.sum(B.mm(other.prec, diff) * diff) -
B.cast(self.dtype, self.dim))
def sample(model, t, noise_f):
"""Sample from a model.
Args:
model (:class:`gpcm.model.AbstractGPCM`): Model to sample from.
t (vector): Time points to sample at.
noise_f (vector): Noise for the sample of the function. Should have the
same size as `t`.
Returns:
tuple[vector]: Tuple containing kernel samples and function samples.
"""
ks, fs = [], []
with wbml.out.Progress(name="Sampling", total=5) as progress:
for i in range(5):
# Sample kernel.
u = B.sample(model.compute_K_u())[:, 0]
K = model.kernel_approx(t, t, u)
wbml.out.kv("Sampled variance", K[0, 0])
K = K / K[0, 0]
ks.append(K[0, :])
# Sample function.
f = B.matmul(B.chol(closest_psd(K)), noise_f)
fs.append(f)
progress()
return ks, fs
def pinv(a: AbstractMatrix):
"""Compute the left pseudo-inverse.
Args:
a (matrix): Matrix to compute left pseudo-inverse of.
Returns:
matrix: Left pseudo-inverse of `a`.
"""
return B.cholsolve(B.chol(B.matmul(a, a, tr_a=True)), B.transpose(a))
def sample(model, t, noise_f):
"""Sample from a model.
Args:
model (:class:`gpcm.model.AbstractGPCM`): Model to sample from.
t (vector): Time points to sample at.
noise_f (vector): Noise for the sample of the function. Should have the
same size as `t`.
Returns:
tuple[vector, ...]: Tuple containing kernel samples, filter samples, and
function samples.
"""
ks, us, fs = [], [], []
# In the below, we look at the third inducing point, because that is the one
# determining the value of the filter at zero: the CGPCM adds two extra inducing
# points to the left.
# Get a smooth sample.
u1 = B.ones(model.n_u)
while B.abs(u1[2]) > 1e-2:
u1 = B.sample(model.compute_K_u())[:, 0]
u = GP(model.k_h())
u = u | (u(model.t_u), u1)
u1_full = u(t).mean.flatten()
# Get a rough sample.
u2 = B.zeros(model.n_u)
while u2[2] < 0.5:
u2 = B.sample(model.compute_K_u())[:, 0]
u = GP(model.k_h())
u = u | (u(model.t_u), u2)
u2_full = u(t).mean.flatten()
with wbml.out.Progress(name="Sampling", total=5) as progress:
for c in [0, 0.1, 0.23, 0.33, 0.5]:
# Sample kernel.
K = model.kernel_approx(t, t, c * u2 + (1 - c) * u1)
wbml.out.kv("Sampled variance", K[0, 0])
K = K / K[0, 0]
ks.append(K[0, :])
# Store filter.
us.append(c * u2_full + (1 - c) * u1_full)
# Sample function.
f = B.matmul(B.chol(closest_psd(K)), noise_f)
fs.append(f)
progress()
return ks, us, fs
def from_normal(cls, dist):
"""Construct from a normal distribution.
Args:
dist (distribution): Normal distribution to construct from.
Returns:
:class:`.NaturalNormal`: Normal distribution parametrised by the natural
parameters of `dist`.
"""
return cls(B.cholsolve(B.chol(dist.var), dist.mean),
B.pd_inv(dist.var))
def sample(self, state: B.RandomState, num: int = 1):
"""Sample.
Args:
state (random state): Random state.
num (int): Number of samples.
Returns:
tuple[random state, tensor]: Random state and sample.
"""
state, noise = Normal(self.prec).sample(state, num)
sample = B.cholsolve(B.chol(self.prec), B.add(noise, self.lam))
# Remove the matrix type if there is no structure. This eases working with
# JITs, which aren't happy with matrix types.
if not structured(sample):
sample = B.dense(sample)
return state, sample
def mean(self):
"""column vector: Mean."""
if self._mean is None:
self._mean = B.cholsolve(B.chol(self.prec), self.lam)
return self._mean
