def _variance(self):
df = tf.convert_to_tensor(self.df)
scale = tf.convert_to_tensor(self.scale)
# We need to put the tf.where inside the outer tf.where to ensure we never
# hit a NaN in the gradient.
denom = tf.where(df > 2., df - 2., tf.ones_like(df))
# Abs(scale) superfluous.
var = (tf.ones(self._batch_shape_tensor(df=df, scale=scale),
dtype=self.dtype)
* tf.square(scale) * df / denom)
# When 1 < df <= 2, variance is infinite.
result_where_defined = tf.where(
df > 2.,
var,
dtype_util.as_numpy_dtype(self.dtype)(np.inf))
if self.allow_nan_stats:
return tf.where(
df > 1.,
result_where_defined,
dtype_util.as_numpy_dtype(self.dtype)(np.nan))
else:
return distribution_util.with_dependencies([
assert_util.assert_less(
tf.ones([], dtype=self.dtype),
df,
message='variance not defined for components of df <= 1'),
], result_where_defined)
def _uniform_unit_norm(dimension, shape, dtype, seed):
"""Returns a batch of points chosen uniformly from the unit hypersphere."""
# This works because the Gaussian distribution is spherically symmetric.
# raw shape: shape + [dimension]
raw = normal.Normal(loc=dtype_util.as_numpy_dtype(dtype)(0),
scale=dtype_util.as_numpy_dtype(dtype)(1)).sample(
tf.concat([shape, [dimension]], axis=0),
seed=seed())
unit_norm = raw / tf.norm(raw, ord=2, axis=-1)[..., tf.newaxis]
return unit_norm
def _assertions(self, t):
if not self.validate_args:
return []
return [
assert_util.assert_greater(
t,
dtype_util.as_numpy_dtype(t.dtype)(-1),
message="Inverse transformation input must be greater than -1."
),
assert_util.assert_less(
t,
dtype_util.as_numpy_dtype(t.dtype)(1),
message="Inverse transformation input must be less than 1.")
]
def _log_cdf(self, y):
low = self._low
high = self._high
# Recall the promise:
# cdf(y) := P[Y <= y]
# = 1, if y >= high,
# = 0, if y < low,
# = P[X <= y], otherwise.
# P[Y <= j] = P[floor(Y) <= j] since mass is only at integers, not in
# between.
j = tf.floor(y)
result_so_far = self.distribution.log_cdf(j)
# Re-define values at the cutoffs.
if low is not None:
result_so_far = tf.where(
j < low,
dtype_util.as_numpy_dtype(self.dtype)(-np.inf), result_so_far)
if high is not None:
result_so_far = tf.where(j >= high, tf.zeros_like(result_so_far),
result_so_far)
return result_so_far
def _log_unnormalized_prob(self, x, log_rate):
# The log-probability at negative points is always -inf.
# Catch such x's and set the output value accordingly.
safe_x = tf.maximum(x if self.interpolate_nondiscrete else tf.floor(x), 0.)
y = safe_x * log_rate - tf.math.lgamma(1. + safe_x)
return tf.where(
tf.equal(x, safe_x), y, dtype_util.as_numpy_dtype(y.dtype)(-np.inf))
def ndtri(p, name="ndtri"):
"""The inverse of the CDF of the Normal distribution function.
Returns x such that the area under the pdf from minus infinity to x is equal
to p.
A piece-wise rational approximation is done for the function.
This is a port of the implementation in netlib.
Args:
p: `Tensor` of type `float32`, `float64`.
name: Python string. A name for the operation (default="ndtri").
Returns:
x: `Tensor` with `dtype=p.dtype`.
Raises:
TypeError: if `p` is not floating-type.
"""
with tf.name_scope(name):
p = tf.convert_to_tensor(p, name="p")
if dtype_util.as_numpy_dtype(p.dtype) not in [np.float32, np.float64]:
raise TypeError(
"p.dtype=%s is not handled, see docstring for supported types."
% p.dtype)
return _ndtri(p)
def ndtr(x, name="ndtr"):
"""Normal distribution function.
Returns the area under the Gaussian probability density function, integrated
from minus infinity to x:
```
1 / x
ndtr(x) = ---------- | exp(-0.5 t**2) dt
sqrt(2 pi) /-inf
= 0.5 (1 + erf(x / sqrt(2)))
= 0.5 erfc(x / sqrt(2))
```
Args:
x: `Tensor` of type `float32`, `float64`.
name: Python string. A name for the operation (default="ndtr").
Returns:
ndtr: `Tensor` with `dtype=x.dtype`.
Raises:
TypeError: if `x` is not floating-type.
"""
with tf.name_scope(name):
x = tf.convert_to_tensor(x, name="x")
if dtype_util.as_numpy_dtype(x.dtype) not in [np.float32, np.float64]:
raise TypeError(
"x.dtype=%s is not handled, see docstring for supported types."
% x.dtype)
return _ndtr(x)
def _log_survival_function(self, y):
low = self._low
high = self._high
# Recall the promise:
# survival_function(y) := P[Y > y]
# = 0, if y >= high,
# = 1, if y < low,
# = P[X > y], otherwise.
# P[Y > j] = P[ceiling(Y) > j] since mass is only at integers, not in
# between.
j = tf.math.ceil(y)
# P[X > j], used when low < X < high.
result_so_far = self.distribution.log_survival_function(j)
# Re-define values at the cutoffs.
if low is not None:
result_so_far = tf.where(j < low, tf.zeros_like(result_so_far),
result_so_far)
if high is not None:
result_so_far = tf.where(
j >= high,
dtype_util.as_numpy_dtype(self.dtype)(-np.inf), result_so_far)
return result_so_far
def _cdf(self, k):
# TODO(b/135263541): Improve numerical precision of categorical.cdf.
probs = self.probs_parameter()
num_categories = self._num_categories(probs)
k, probs = _broadcast_cat_event_and_params(
k, probs, base_dtype=dtype_util.base_dtype(self.dtype))
# Since the lowest number in the support is 0, any k < 0 should be zero in
# the output.
should_be_zero = k < 0
# Will use k as an index in the gather below, so clip it to {0,...,K-1}.
k = tf.clip_by_value(tf.cast(k, tf.int32), 0, num_categories - 1)
batch_shape = tf.shape(k)
# tf.gather(..., batch_dims=batch_dims) requires static batch_dims kwarg, so
# to handle the case where the batch shape is dynamic, flatten the batch
# dims (so we know batch_dims=1).
k_flat_batch = tf.reshape(k, [-1])
probs_flat_batch = tf.reshape(
probs, tf.concat(([-1], [num_categories]), axis=0))
cdf_flat = tf.gather(tf.cumsum(probs_flat_batch, axis=-1),
k_flat_batch[..., tf.newaxis],
batch_dims=1)
cdf = tf.reshape(cdf_flat, shape=batch_shape)
zero = np.array(0, dtype=dtype_util.as_numpy_dtype(cdf.dtype))
return tf.where(should_be_zero, zero, cdf)
def _kl_uniform_uniform(a, b, name=None):
"""Calculate the batched KL divergence KL(a || b) with a and b Uniform.
Note that the KL divergence is infinite if the support of `a` is not a subset
of the support of `b`.
Args:
a: instance of a Uniform distribution object.
b: instance of a Uniform distribution object.
name: (optional) Name to use for created operations.
default is "kl_uniform_uniform".
Returns:
Batchwise KL(a || b)
"""
with tf.name_scope(name or 'kl_uniform_uniform'):
# Consistent with
# http://www.mast.queensu.ca/~communications/Papers/gil-msc11.pdf, page 60
# Watch out for the change in conventions--they use 'a' and 'b' to refer to
# lower and upper bounds respectively there.
dtype = dtype_util.common_dtype([a.low, a.high, b.low, b.high],
tf.float32)
a_low = tf.convert_to_tensor(a.low)
b_low = tf.convert_to_tensor(b.low)
a_high = tf.convert_to_tensor(a.high)
b_high = tf.convert_to_tensor(b.high)
return tf.where(
(b_low <= a_low) & (a_high <= b_high),
tf.math.log(b_high - b_low) - tf.math.log(a_high - a_low),
dtype_util.as_numpy_dtype(dtype)(np.inf))
def _get_shape(x, out_type=tf.int32):
# Return the shape of a Tensor or a SparseTensor as an np.array if its shape
# is known statically. Otherwise return a Tensor representing the shape.
if tensorshape_util.is_fully_defined(x.shape):
return np.array(tensorshape_util.as_list(x.shape),
dtype=dtype_util.as_numpy_dtype(out_type))
return tf.shape(x, out_type=out_type)
def _entropy(self):
logits, probs = self._logits_and_probs_no_checks()
if not self.validate_args:
assertions = []
else:
assertions = [
assert_util.assert_less(
probs,
dtype_util.as_numpy_dtype(self.dtype)(1.),
message=
'Entropy is undefined when logits = inf or probs = 1.')
]
with tf.control_dependencies(assertions):
# Claim: entropy(p) = softplus(s)/p - s
# where s=logits and p=probs.
#
# Proof:
#
# entropy(p)
# := -[(1-p)log(1-p) + plog(p)]/p
# = -[log(1-p) + plog(p/(1-p))]/p
# = -[-softplus(s) + ps]/p
# = softplus(s)/p - s
#
# since,
# log[1-sigmoid(s)]
# = log[1/(1+exp(s)]
# = -log[1+exp(s)]
# = -softplus(s)
#
# using the fact that,
# 1-sigmoid(s) = sigmoid(-s) = 1/(1+exp(s))
return tf.math.softplus(logits) / probs - logits
def _log_prob(self, x, power=None):
# The log probability at positive integer points x is log(x^(-power) / Z)
# where Z is the normalization constant. For x < 1 and non-integer points,
# the log-probability is -inf.
#
# However, if interpolate_nondiscrete is True, we return the natural
# continuous relaxation for x >= 1 which agrees with the log probability at
# positive integer points.
#
# If interpolate_nondiscrete is False and validate_args is True, we check
# that the sample point x is in the support. That is, x is equivalent to a
# positive integer.
power = power if power is not None else tf.convert_to_tensor(
self.power)
x = tf.cast(x, power.dtype)
if self.validate_args and not self.interpolate_nondiscrete:
x = distribution_util.embed_check_integer_casting_closed(
x, target_dtype=self.dtype, assert_positive=True)
log_normalization = tf.math.log(tf.math.zeta(power, 1.))
safe_x = tf.maximum(x if self.interpolate_nondiscrete else tf.floor(x),
1.)
y = -power * tf.math.log(safe_x)
log_unnormalized_prob = tf.where(
tf.equal(x, safe_x), y,
dtype_util.as_numpy_dtype(y.dtype)(-np.inf))
return log_unnormalized_prob - log_normalization
def log1psquare(x, name=None):
"""Numerically stable calculation of `log(1 + x**2)` for small or large `|x|`.
For sufficiently large `x` we use the following observation:
```none
log(1 + x**2) = 2 log(|x|) + log(1 + 1 / x**2)
--> 2 log(|x|) as x --> inf
```
Numerically, `log(1 + 1 / x**2)` is `0` when `1 / x**2` is small relative to
machine epsilon.
Args:
x: Float `Tensor` input.
name: Python string indicating the name of the TensorFlow operation.
Default value: `'log1psquare'`.
Returns:
log1psq: Float `Tensor` representing `log(1. + x**2.)`.
"""
with tf.name_scope(name or 'log1psquare'):
x = tf.convert_to_tensor(x, dtype_hint=tf.float32, name='x')
dtype = dtype_util.as_numpy_dtype(x.dtype)
eps = np.finfo(dtype).eps.astype(np.float64)
is_large = tf.abs(x) > (eps**-0.5).astype(dtype)
# Mask out small x's so the gradient correctly propagates.
abs_large_x = tf.where(is_large, tf.abs(x), tf.ones([], x.dtype))
return tf.where(is_large, 2. * tf.math.log(abs_large_x),
tf.math.log1p(tf.square(x)))
def _kl_pareto_pareto(a, b, name=None):
"""Calculate the batched KL divergence KL(a || b) with a and b Pareto.
Args:
a: instance of a Pareto distribution object.
b: instance of a Pareto distribution object.
name: (optional) Name to use for created operations.
default is 'kl_pareto_pareto'.
Returns:
Batchwise KL(a || b)
"""
with tf.name_scope(name or 'kl_pareto_pareto'):
# Consistent with
# http://www.mast.queensu.ca/~communications/Papers/gil-msc11.pdf, page 55
# Terminology is different from source to source for Pareto distributions.
# The 'concentration' parameter corresponds to 'a' in that source, and the
# 'scale' parameter corresponds to 'm'.
a_scale = tf.convert_to_tensor(a.scale)
b_scale = tf.convert_to_tensor(b.scale)
a_concentration = tf.convert_to_tensor(a.concentration)
b_concentration = tf.convert_to_tensor(b.concentration)
return tf.where(
a_scale >= b_scale,
(b_concentration * (tf.math.log(a_scale) - tf.math.log(b_scale)) +
tf.math.log(a_concentration) - tf.math.log(b_concentration) +
b_concentration / a_concentration - 1.),
dtype_util.as_numpy_dtype(a.dtype)(np.inf))
def _extend_support(self, x, scale, f, alt):
"""Returns `f(x)` if x is in the support, and `alt` otherwise.
Given `f` which is defined on the support of this distribution
(e.g. x > scale), extend the function definition to the real line
by defining `f(x) = alt` for `x < scale`.
Args:
x: Floating-point Tensor to evaluate `f` at.
scale: Floating-point Tensor by which to verify `x` validity.
f: Lambda that takes in a tensor and returns a tensor. This represents the
function who we want to extend the domain of definition.
alt: Python or numpy literal representing the value to use for extending
the domain.
Returns:
Tensor representing an extension of `f(x)`.
"""
if self.validate_args:
return f(x)
scale = tf.convert_to_tensor(self.scale) if scale is None else scale
is_invalid = x < scale
# We need to do this to ensure gradients are sound.
y = f(tf.where(is_invalid, scale, x))
if alt == 0.:
alt = tf.zeros([], dtype=y.dtype)
elif alt == 1.:
alt = tf.ones([], dtype=y.dtype)
else:
alt = dtype_util.as_numpy_dtype(self.dtype)(alt)
return tf.where(is_invalid, alt, y)
def matrix_rank(a, tol=None, validate_args=False, name=None):
"""Compute the matrix rank; the number of non-zero SVD singular values.
Arguments:
a: (Batch of) `float`-like matrix-shaped `Tensor`(s) which are to be
pseudo-inverted.
tol: Threshold below which the singular value is counted as 'zero'.
Default value: `None` (i.e., `eps * max(rows, cols) * max(singular_val)`).
validate_args: When `True`, additional assertions might be embedded in the
graph.
Default value: `False` (i.e., no graph assertions are added).
name: Python `str` prefixed to ops created by this function.
Default value: 'matrix_rank'.
Returns:
matrix_rank: (Batch of) `int32` scalars representing the number of non-zero
singular values.
"""
with tf.name_scope(name or 'matrix_rank'):
a = tf.convert_to_tensor(a, dtype_hint=tf.float32, name='a')
assertions = _maybe_validate_matrix(a, validate_args)
if assertions:
with tf.control_dependencies(assertions):
a = tf.identity(a)
s = tf.linalg.svd(a, compute_uv=False)
if tol is None:
if tensorshape_util.is_fully_defined(a.shape[-2:]):
m = np.max(a.shape[-2:].as_list())
else:
m = tf.reduce_max(tf.shape(a)[-2:])
eps = np.finfo(dtype_util.as_numpy_dtype(a.dtype)).eps
tol = (eps * tf.cast(m, a.dtype) *
tf.reduce_max(s, axis=-1, keepdims=True))
return tf.reduce_sum(tf.cast(s > tol, tf.int32), axis=-1)
def _assertions(self, t):
if not self.validate_args:
return []
return [
assert_util.assert_none_equal(
t,
dtype_util.as_numpy_dtype(t.dtype)(0.),
message="All elements must be non-zero.")
]
def _log_prob(self, x):
log_prob = -(0.5 * (
(x - self.loc) / self.scale)**2 + 0.5 * np.log(2. * np.pi) +
tf.math.log(self.scale * self._normalizer))
# p(x) is 0 outside the bounds.
bounded_log_prob = tf.where(
(x > self._high) | (x < self._low),
dtype_util.as_numpy_dtype(x.dtype)(-np.inf), log_prob)
return bounded_log_prob
def grad(dy):
"""Computes a derivative for the min and max parameters.
This function implements the derivative wrt the truncation bounds, which
get blocked by the sampler. We use a custom expression for numerical
stability instead of automatic differentiation on CDF for implicit
gradients.
Args:
dy: output gradients
Returns:
The standard normal samples and the gradients wrt the upper
bound and lower bound.
"""
# std_samples has an extra dimension (the sample dimension), expand
# lower and upper so they broadcast along this dimension.
# See note above regarding parameterized_truncated_normal, the sample
# dimension is the final dimension.
lower_broadcast = lower[..., tf.newaxis]
upper_broadcast = upper[..., tf.newaxis]
cdf_samples = ((special_math.ndtr(std_samples) -
special_math.ndtr(lower_broadcast)) /
(special_math.ndtr(upper_broadcast) -
special_math.ndtr(lower_broadcast)))
# tiny, eps are tolerance parameters to ensure we stay away from giving
# a zero arg to the log CDF expression.
tiny = np.finfo(dtype_util.as_numpy_dtype(self.dtype)).tiny
eps = np.finfo(dtype_util.as_numpy_dtype(self.dtype)).eps
cdf_samples = tf.clip_by_value(cdf_samples, tiny, 1 - eps)
du = tf.exp(0.5 * (std_samples**2 - upper_broadcast**2) +
tf.math.log(cdf_samples))
dl = tf.exp(0.5 * (std_samples**2 - lower_broadcast**2) +
tf.math.log1p(-cdf_samples))
# Reduce the gradient across the samples
grad_u = tf.reduce_sum(dy * du, axis=-1)
grad_l = tf.reduce_sum(dy * dl, axis=-1)
return [grad_l, grad_u]
def _log_cdf(self, x):
loc = tf.convert_to_tensor(self.loc)
scale = tf.convert_to_tensor(self.scale)
with tf.control_dependencies(self._maybe_assert_valid_sample(x, loc)):
safe_x = self._get_safe_input(x, loc=loc, scale=scale)
log_cdf = np.log(2 / np.pi) + tf.math.log(
tf.atan((safe_x - loc) / scale))
return tf.where(x < loc,
dtype_util.as_numpy_dtype(self.dtype)(-np.inf),
log_cdf)
def _log_prob(self, x):
log_rate = self._log_rate_parameter_no_checks()
log_probs = (self._log_unnormalized_prob(x, log_rate) -
self._log_normalization(log_rate))
if not self.interpolate_nondiscrete:
# Ensure the gradient wrt `rate` is zero at non-integer points.
log_probs = tf.where(
tf.math.is_inf(log_probs),
dtype_util.as_numpy_dtype(log_probs.dtype)(-np.inf),
log_probs)
return log_probs
def _parameter_control_dependencies(self, is_init):
if not self.validate_args:
return []
assertions = []
if (self.hinge_softness is not None
and is_init != tensor_util.is_ref(self.hinge_softness)):
assertions.append(
assert_util.assert_none_equal(
dtype_util.as_numpy_dtype(self._hinge_softness.dtype)(0),
self.hinge_softness,
message='Argument `hinge_softness` must be non-zero.'))
return assertions
def softplus_inverse(x, name=None):
"""Computes the inverse softplus, i.e., x = softplus_inverse(softplus(x)).
Mathematically this op is equivalent to:
```none
softplus_inverse = log(exp(x) - 1.)
```
Args:
x: `Tensor`. Non-negative (not enforced), floating-point.
name: A name for the operation (optional).
Returns:
`Tensor`. Has the same type/shape as input `x`.
"""
with tf.name_scope(name or 'softplus_inverse'):
x = tf.convert_to_tensor(x, name='x')
# We begin by deriving a more numerically stable softplus_inverse:
# x = softplus(y) = Log[1 + exp{y}], (which means x > 0).
# ==> exp{x} = 1 + exp{y} (1)
# ==> y = Log[exp{x} - 1] (2)
# = Log[(exp{x} - 1) / exp{x}] + Log[exp{x}]
# = Log[(1 - exp{-x}) / 1] + Log[exp{x}]
# = Log[1 - exp{-x}] + x (3)
# (2) is the "obvious" inverse, but (3) is more stable than (2) for large x.
# For small x (e.g. x = 1e-10), (3) will become -inf since 1 - exp{-x} will
# be zero. To fix this, we use 1 - exp{-x} approx x for small x > 0.
#
# In addition to the numerically stable derivation above, we clamp
# small/large values to be congruent with the logic in:
# tensorflow/core/kernels/softplus_op.h
#
# Finally, we set the input to one whenever the input is too large or too
# small. This ensures that no unchosen codepath is +/- inf. This is
# necessary to ensure the gradient doesn't get NaNs. Recall that the
# gradient of `where` behaves like `pred*pred_true + (1-pred)*pred_false`
# thus an `inf` in an unselected path results in `0*inf=nan`. We are careful
# to overwrite `x` with ones only when we will never actually use this
# value. Note that we use ones and not zeros since `log(expm1(0.)) = -inf`.
threshold = np.log(np.finfo(dtype_util.as_numpy_dtype(x.dtype)).eps) + 2.
is_too_small = x < np.exp(threshold)
is_too_large = x > -threshold
too_small_value = tf.math.log(x)
too_large_value = x
# This `where` will ultimately be a NOP because we won't select this
# codepath whenever we used the surrogate `ones_like`.
x = tf.where(is_too_small | is_too_large, tf.ones([], x.dtype), x)
y = x + tf.math.log(-tf.math.expm1(-x)) # == log(expm1(x))
return tf.where(is_too_small,
too_small_value,
tf.where(is_too_large, too_large_value, y))
def _validate_correlationness(self, x):
if not self.validate_args or self.input_output_cholesky:
return x
checks = [
assert_util.assert_less_equal(
dtype_util.as_numpy_dtype(x.dtype)(-1),
x,
message='Correlations must be >= -1.'),
assert_util.assert_less_equal(
x,
dtype_util.as_numpy_dtype(x.dtype)(1),
message='Correlations must be <= 1.'),
assert_util.assert_near(tf.linalg.diag_part(x),
dtype_util.as_numpy_dtype(x.dtype)(1),
message='Self-correlations must be = 1.'),
assert_util.assert_near(
x,
tf.linalg.matrix_transpose(x),
message='Correlation matrices must be symmetric')
]
with tf.control_dependencies(checks):
return tf.identity(x)
def maybe_assert_categorical_param_correctness(is_init, validate_args, probs,
logits):
"""Return assertions for `Categorical`-type distributions."""
assertions = []
# In init, we can always build shape and dtype checks because
# we assume shape doesn't change for Variable backed args.
if is_init:
x, name = (probs, 'probs') if logits is None else (logits, 'logits')
if not dtype_util.is_floating(x.dtype):
raise TypeError(
'Argument `{}` must having floating type.'.format(name))
msg = 'Argument `{}` must have rank at least 1.'.format(name)
ndims = tensorshape_util.rank(x.shape)
if ndims is not None:
if ndims < 1:
raise ValueError(msg)
elif validate_args:
x = tf.convert_to_tensor(x)
probs = x if logits is None else None # Retain tensor conversion.
logits = x if probs is None else None
assertions.append(
assert_util.assert_rank_at_least(x, 1, message=msg))
if not validate_args:
assert not assertions # Should never happen.
return []
if logits is not None:
if is_init != tensor_util.is_ref(logits):
logits = tf.convert_to_tensor(logits)
assertions.extend(
distribution_util.assert_categorical_event_shape(logits))
if probs is not None:
if is_init != tensor_util.is_ref(probs):
probs = tf.convert_to_tensor(probs)
assertions.extend([
assert_util.assert_non_negative(probs),
assert_util.assert_near(
tf.reduce_sum(probs, axis=-1),
np.array(1, dtype=dtype_util.as_numpy_dtype(probs.dtype)),
message='Argument `probs` must sum to 1.')
])
assertions.extend(
distribution_util.assert_categorical_event_shape(probs))
return assertions
def _assertions(self, t):
if not self.validate_args:
return []
return [
assert_util.assert_non_negative(
t,
message="Inverse transformation input must be greater than 0."
),
assert_util.assert_less_equal(
t,
dtype_util.as_numpy_dtype(t.dtype)(1.),
message=
"Inverse transformation input must be less than or equal "
"to 1.")
]
def _mode(self):
concentration = tf.convert_to_tensor(self.concentration)
rate = tf.convert_to_tensor(self.rate)
mode = (concentration - 1.) / rate
if self.allow_nan_stats:
assertions = []
else:
assertions = [assert_util.assert_less(
tf.ones([], self.dtype), concentration,
message='Mode not defined when any concentration <= 1.')]
with tf.control_dependencies(assertions):
return tf.where(
concentration > 1.,
mode,
dtype_util.as_numpy_dtype(self.dtype)(np.nan))
def _mode(self):
df = tf.convert_to_tensor(self.df)
mode = df - 2.
if self.allow_nan_stats:
assertions = []
else:
assertions = [
assert_util.assert_less(
2. * tf.ones([], self.dtype),
df,
message='Mode not defined when df <= 2.')
]
with tf.control_dependencies(assertions):
return tf.where(df > 2., mode,
dtype_util.as_numpy_dtype(self.dtype)(np.nan))
def _mean(self):
concentration = tf.convert_to_tensor(self.concentration)
scale = tf.convert_to_tensor(self.scale)
mean = scale / (concentration - 1.)
if self.allow_nan_stats:
assertions = []
else:
assertions = [
assert_util.assert_less(
tf.ones([], self.dtype),
concentration,
message='mean undefined when any concentration <= 1')
]
with tf.control_dependencies(assertions):
return tf.where(concentration > 1., mean,
dtype_util.as_numpy_dtype(self.dtype)(np.nan))
