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from numbers import Number
import torch
from torch.distributions import constraints
from torch.distributions.distribution import Distribution
from torch.distributions.utils import broadcast_all
class Uniform(Distribution):
r"""
Generates uniformly distributed random samples from the half-open interval
``[low, high)``.
Example::
>>> m = Uniform(torch.tensor([0.0]), torch.tensor([5.0]))
>>> m.sample() # uniformly distributed in the range [0.0, 5.0)
tensor([ 2.3418])
Args:
low (float or Tensor): lower range (inclusive).
high (float or Tensor): upper range (exclusive).
"""
# TODO allow (loc,scale) parameterization to allow independent constraints.
arg_constraints = {'low': constraints.dependent, 'high': constraints.dependent}
has_rsample = True
@property
def mean(self):
return (self.high + self.low) / 2
@property
def stddev(self):
return (self.high - self.low) / 12**0.5
@property
def variance(self):
return (self.high - self.low).pow(2) / 12
def __init__(self, low, high, validate_args=None):
self.low, self.high = broadcast_all(low, high)
if isinstance(low, Number) and isinstance(high, Number):
batch_shape = torch.Size()
else:
batch_shape = self.low.size()
super(Uniform, self).__init__(batch_shape, validate_args=validate_args)
if self._validate_args and not torch.lt(self.low, self.high).all():
raise ValueError("Uniform is not defined when low>= high")
def expand(self, batch_shape, _instance=None):
new = self._get_checked_instance(Uniform, _instance)
batch_shape = torch.Size(batch_shape)
new.low = self.low.expand(batch_shape)
new.high = self.high.expand(batch_shape)
super(Uniform, new).__init__(batch_shape, validate_args=False)
new._validate_args = self._validate_args
return new
@constraints.dependent_property
def support(self):
return constraints.interval(self.low, self.high)
def rsample(self, sample_shape=torch.Size()):
shape = self._extended_shape(sample_shape)
rand = torch.rand(shape, dtype=self.low.dtype, device=self.low.device)
return self.low + rand * (self.high - self.low)
def log_prob(self, value):
if self._validate_args:
self._validate_sample(value)
lb = value.ge(self.low).type_as(self.low)
ub = value.lt(self.high).type_as(self.low)
return torch.log(lb.mul(ub)) - torch.log(self.high - self.low)
def cdf(self, value):
if self._validate_args:
self._validate_sample(value)
result = (value - self.low) / (self.high - self.low)
return result.clamp(min=0, max=1)
def icdf(self, value):
if self._validate_args:
self._validate_sample(value)
result = value * (self.high - self.low) + self.low
return result
def entropy(self):
return torch.log(self.high - self.low)
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