pytorch/torch/nn/modules/dropout.py

import torch.nn.functional as F
from torch import Tensor

from .module import Module


__all__ = [
    "Dropout",
    "Dropout1d",
    "Dropout2d",
    "Dropout3d",
    "AlphaDropout",
    "FeatureAlphaDropout",
]


class _DropoutNd(Module):
    __constants__ = ["p", "inplace"]
    p: float
    inplace: bool

    def __init__(self, p: float = 0.5, inplace: bool = False) -> None:
        super().__init__()
        if p < 0 or p > 1:
            raise ValueError(
                f"dropout probability has to be between 0 and 1, but got {p}"
            )
        self.p = p
        self.inplace = inplace

    def extra_repr(self) -> str:
        return f"p={self.p}, inplace={self.inplace}"


class Dropout(_DropoutNd):
    r"""During training, randomly zeroes some of the elements of the input tensor with probability :attr:`p`.

    The zeroed elements are chosen independently for each forward call and are sampled from a Bernoulli distribution.

    Each channel will be zeroed out independently on every forward call.

    This has proven to be an effective technique for regularization and
    preventing the co-adaptation of neurons as described in the paper
    `Improving neural networks by preventing co-adaptation of feature
    detectors`_ .

    Furthermore, the outputs are scaled by a factor of :math:`\frac{1}{1-p}` during
    training. This means that during evaluation the module simply computes an
    identity function.

    Args:
        p: probability of an element to be zeroed. Default: 0.5
        inplace: If set to ``True``, will do this operation in-place. Default: ``False``

    Shape:
        - Input: :math:`(*)`. Input can be of any shape
        - Output: :math:`(*)`. Output is of the same shape as input

    Examples::

        >>> m = nn.Dropout(p=0.2)
        >>> input = torch.randn(20, 16)
        >>> output = m(input)

    .. _Improving neural networks by preventing co-adaptation of feature
        detectors: https://arxiv.org/abs/1207.0580
    """

    def forward(self, input: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.dropout(input, self.p, self.training, self.inplace)


class Dropout1d(_DropoutNd):
    r"""Randomly zero out entire channels.

    A channel is a 1D feature map,
    e.g., the :math:`j`-th channel of the :math:`i`-th sample in the
    batched input is a 1D tensor :math:`\text{input}[i, j]`.

    Each channel will be zeroed out independently on every forward call with
    probability :attr:`p` using samples from a Bernoulli distribution.

    Usually the input comes from :class:`nn.Conv1d` modules.

    As described in the paper
    `Efficient Object Localization Using Convolutional Networks`_ ,
    if adjacent pixels within feature maps are strongly correlated
    (as is normally the case in early convolution layers) then i.i.d. dropout
    will not regularize the activations and will otherwise just result
    in an effective learning rate decrease.

    In this case, :func:`nn.Dropout1d` will help promote independence between
    feature maps and should be used instead.

    Args:
        p (float, optional): probability of an element to be zero-ed.
        inplace (bool, optional): If set to ``True``, will do this operation
            in-place

    Shape:
        - Input: :math:`(N, C, L)` or :math:`(C, L)`.
        - Output: :math:`(N, C, L)` or :math:`(C, L)` (same shape as input).

    Examples::

        >>> m = nn.Dropout1d(p=0.2)
        >>> input = torch.randn(20, 16, 32)
        >>> output = m(input)

    .. _Efficient Object Localization Using Convolutional Networks:
       https://arxiv.org/abs/1411.4280
    """

    def forward(self, input: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.dropout1d(input, self.p, self.training, self.inplace)


class Dropout2d(_DropoutNd):
    r"""Randomly zero out entire channels.

    A channel is a 2D feature map,
    e.g., the :math:`j`-th channel of the :math:`i`-th sample in the
    batched input is a 2D tensor :math:`\text{input}[i, j]`.

    Each channel will be zeroed out independently on every forward call with
    probability :attr:`p` using samples from a Bernoulli distribution.

    Usually the input comes from :class:`nn.Conv2d` modules.

    As described in the paper
    `Efficient Object Localization Using Convolutional Networks`_ ,
    if adjacent pixels within feature maps are strongly correlated
    (as is normally the case in early convolution layers) then i.i.d. dropout
    will not regularize the activations and will otherwise just result
    in an effective learning rate decrease.

    In this case, :func:`nn.Dropout2d` will help promote independence between
    feature maps and should be used instead.

    Args:
        p (float, optional): probability of an element to be zero-ed.
        inplace (bool, optional): If set to ``True``, will do this operation
            in-place

    .. warning ::
        Due to historical reasons, this class will perform 1D channel-wise dropout
        for 3D inputs (as done by :class:`nn.Dropout1d`). Thus, it currently does NOT
        support inputs without a batch dimension of shape :math:`(C, H, W)`. This
        behavior will change in a future release to interpret 3D inputs as no-batch-dim
        inputs. To maintain the old behavior, switch to :class:`nn.Dropout1d`.

    Shape:
        - Input: :math:`(N, C, H, W)` or :math:`(N, C, L)`.
        - Output: :math:`(N, C, H, W)` or :math:`(N, C, L)` (same shape as input).

    Examples::

        >>> m = nn.Dropout2d(p=0.2)
        >>> input = torch.randn(20, 16, 32, 32)
        >>> output = m(input)

    .. _Efficient Object Localization Using Convolutional Networks:
       https://arxiv.org/abs/1411.4280
    """

    def forward(self, input: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.dropout2d(input, self.p, self.training, self.inplace)


class Dropout3d(_DropoutNd):
    r"""Randomly zero out entire channels.

    A channel is a 3D feature map,
    e.g., the :math:`j`-th channel of the :math:`i`-th sample in the
    batched input is a 3D tensor :math:`\text{input}[i, j]`.

    Each channel will be zeroed out independently on every forward call with
    probability :attr:`p` using samples from a Bernoulli distribution.

    Usually the input comes from :class:`nn.Conv3d` modules.

    As described in the paper
    `Efficient Object Localization Using Convolutional Networks`_ ,
    if adjacent pixels within feature maps are strongly correlated
    (as is normally the case in early convolution layers) then i.i.d. dropout
    will not regularize the activations and will otherwise just result
    in an effective learning rate decrease.

    In this case, :func:`nn.Dropout3d` will help promote independence between
    feature maps and should be used instead.

    Args:
        p (float, optional): probability of an element to be zeroed.
        inplace (bool, optional): If set to ``True``, will do this operation
            in-place

    Shape:
        - Input: :math:`(N, C, D, H, W)` or :math:`(C, D, H, W)`.
        - Output: :math:`(N, C, D, H, W)` or :math:`(C, D, H, W)` (same shape as input).

    Examples::

        >>> m = nn.Dropout3d(p=0.2)
        >>> input = torch.randn(20, 16, 4, 32, 32)
        >>> output = m(input)

    .. _Efficient Object Localization Using Convolutional Networks:
       https://arxiv.org/abs/1411.4280
    """

    def forward(self, input: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.dropout3d(input, self.p, self.training, self.inplace)


class AlphaDropout(_DropoutNd):
    r"""Applies Alpha Dropout over the input.

    Alpha Dropout is a type of Dropout that maintains the self-normalizing
    property.
    For an input with zero mean and unit standard deviation, the output of
    Alpha Dropout maintains the original mean and standard deviation of the
    input.
    Alpha Dropout goes hand-in-hand with SELU activation function, which ensures
    that the outputs have zero mean and unit standard deviation.

    During training, it randomly masks some of the elements of the input
    tensor with probability *p* using samples from a bernoulli distribution.
    The elements to masked are randomized on every forward call, and scaled
    and shifted to maintain zero mean and unit standard deviation.

    During evaluation the module simply computes an identity function.

    More details can be found in the paper `Self-Normalizing Neural Networks`_ .

    Args:
        p (float): probability of an element to be dropped. Default: 0.5
        inplace (bool, optional): If set to ``True``, will do this operation
            in-place

    Shape:
        - Input: :math:`(*)`. Input can be of any shape
        - Output: :math:`(*)`. Output is of the same shape as input

    Examples::

        >>> m = nn.AlphaDropout(p=0.2)
        >>> input = torch.randn(20, 16)
        >>> output = m(input)

    .. _Self-Normalizing Neural Networks: https://arxiv.org/abs/1706.02515
    """

    def forward(self, input: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.alpha_dropout(input, self.p, self.training)


class FeatureAlphaDropout(_DropoutNd):
    r"""Randomly masks out entire channels.

    A channel is a feature map,
    e.g. the :math:`j`-th channel of the :math:`i`-th sample in the batch input
    is a tensor :math:`\text{input}[i, j]` of the input tensor). Instead of
    setting activations to zero, as in regular Dropout, the activations are set
    to the negative saturation value of the SELU activation function. More details
    can be found in the paper `Self-Normalizing Neural Networks`_ .

    Each element will be masked independently for each sample on every forward
    call with probability :attr:`p` using samples from a Bernoulli distribution.
    The elements to be masked are randomized on every forward call, and scaled
    and shifted to maintain zero mean and unit variance.

    Usually the input comes from :class:`nn.AlphaDropout` modules.

    As described in the paper
    `Efficient Object Localization Using Convolutional Networks`_ ,
    if adjacent pixels within feature maps are strongly correlated
    (as is normally the case in early convolution layers) then i.i.d. dropout
    will not regularize the activations and will otherwise just result
    in an effective learning rate decrease.

    In this case, :func:`nn.AlphaDropout` will help promote independence between
    feature maps and should be used instead.

    Args:
        p (float, optional): probability of an element to be zeroed. Default: 0.5
        inplace (bool, optional): If set to ``True``, will do this operation
            in-place

    Shape:
        - Input: :math:`(N, C, D, H, W)` or :math:`(C, D, H, W)`.
        - Output: :math:`(N, C, D, H, W)` or :math:`(C, D, H, W)` (same shape as input).

    Examples::

        >>> m = nn.FeatureAlphaDropout(p=0.2)
        >>> input = torch.randn(20, 16, 4, 32, 32)
        >>> output = m(input)

    .. _Self-Normalizing Neural Networks: https://arxiv.org/abs/1706.02515
    .. _Efficient Object Localization Using Convolutional Networks:
       https://arxiv.org/abs/1411.4280
    """

    def forward(self, input: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.feature_alpha_dropout(input, self.p, self.training)