/usr/local/lib64/python3.6/site-packages/torch/distributions
Edit: /usr/local/lib64/python3.6/site-packages/torch/distributions/categorical.py (5488B)
import torch
from torch._six import nan
from torch.distributions import constraints
from torch.distributions.distribution import Distribution
from torch.distributions.utils import probs_to_logits, logits_to_probs, lazy_property
class Categorical(Distribution):
r"""
Creates a categorical distribution parameterized by either :attr:`probs` or
:attr:`logits` (but not both).
.. note::
It is equivalent to the distribution that :func:`torch.multinomial`
samples from.
Samples are integers from :math:`\{0, \ldots, K-1\}` where `K` is ``probs.size(-1)``.
If `probs` is 1-dimensional with length-`K`, each element is the relative probability
of sampling the class at that index.
If `probs` is N-dimensional, the first N-1 dimensions are treated as a batch of
relative probability vectors.
.. note:: The `probs` argument must be non-negative, finite and have a non-zero sum,
and it will be normalized to sum to 1 along the last dimension. :attr:`probs`
will return this normalized value.
The `logits` argument will be interpreted as unnormalized log probabilities
and can therefore be any real number. It will likewise be normalized so that
the resulting probabilities sum to 1 along the last dimension. :attr:`logits`
will return this normalized value.
See also: :func:`torch.multinomial`
Example::
>>> m = Categorical(torch.tensor([ 0.25, 0.25, 0.25, 0.25 ]))
>>> m.sample() # equal probability of 0, 1, 2, 3
tensor(3)
Args:
probs (Tensor): event probabilities
logits (Tensor): event log probabilities (unnormalized)
"""
arg_constraints = {'probs': constraints.simplex,
'logits': constraints.real_vector}
has_enumerate_support = True
def __init__(self, probs=None, logits=None, validate_args=None):
if (probs is None) == (logits is None):
raise ValueError("Either `probs` or `logits` must be specified, but not both.")
if probs is not None:
if probs.dim() < 1:
raise ValueError("`probs` parameter must be at least one-dimensional.")
self.probs = probs / probs.sum(-1, keepdim=True)
else:
if logits.dim() < 1:
raise ValueError("`logits` parameter must be at least one-dimensional.")
# Normalize
self.logits = logits - logits.logsumexp(dim=-1, keepdim=True)
self._param = self.probs if probs is not None else self.logits
self._num_events = self._param.size()[-1]
batch_shape = self._param.size()[:-1] if self._param.ndimension() > 1 else torch.Size()
super(Categorical, self).__init__(batch_shape, validate_args=validate_args)
def expand(self, batch_shape, _instance=None):
new = self._get_checked_instance(Categorical, _instance)
batch_shape = torch.Size(batch_shape)
param_shape = batch_shape + torch.Size((self._num_events,))
if 'probs' in self.__dict__:
new.probs = self.probs.expand(param_shape)
new._param = new.probs
if 'logits' in self.__dict__:
new.logits = self.logits.expand(param_shape)
new._param = new.logits
new._num_events = self._num_events
super(Categorical, new).__init__(batch_shape, validate_args=False)
new._validate_args = self._validate_args
return new
def _new(self, *args, **kwargs):
return self._param.new(*args, **kwargs)
@constraints.dependent_property(is_discrete=True, event_dim=0)
def support(self):
return constraints.integer_interval(0, self._num_events - 1)
@lazy_property
def logits(self):
return probs_to_logits(self.probs)
@lazy_property
def probs(self):
return logits_to_probs(self.logits)
@property
def param_shape(self):
return self._param.size()
@property
def mean(self):
return torch.full(self._extended_shape(), nan, dtype=self.probs.dtype, device=self.probs.device)
@property
def variance(self):
return torch.full(self._extended_shape(), nan, dtype=self.probs.dtype, device=self.probs.device)
def sample(self, sample_shape=torch.Size()):
if not isinstance(sample_shape, torch.Size):
sample_shape = torch.Size(sample_shape)
probs_2d = self.probs.reshape(-1, self._num_events)
samples_2d = torch.multinomial(probs_2d, sample_shape.numel(), True).T
return samples_2d.reshape(self._extended_shape(sample_shape))
def log_prob(self, value):
if self._validate_args:
self._validate_sample(value)
value = value.long().unsqueeze(-1)
value, log_pmf = torch.broadcast_tensors(value, self.logits)
value = value[..., :1]
return log_pmf.gather(-1, value).squeeze(-1)
def entropy(self):
min_real = torch.finfo(self.logits.dtype).min
logits = torch.clamp(self.logits, min=min_real)
p_log_p = logits * self.probs
return -p_log_p.sum(-1)
def enumerate_support(self, expand=True):
num_events = self._num_events
values = torch.arange(num_events, dtype=torch.long, device=self._param.device)
values = values.view((-1,) + (1,) * len(self._batch_shape))
if expand:
values = values.expand((-1,) + self._batch_shape)
return values