torch/nn/modules/linear.py

# mypy: allow-untyped-defs
import math
from typing import Any

import torch
from torch import Tensor
from torch.nn import functional as F, init
from torch.nn.parameter import Parameter, UninitializedParameter

from .lazy import LazyModuleMixin
from .module import Module


__all__ = [
    "Bilinear",
    "Identity",
    "LazyLinear",
    "Linear",
]


class Identity(Module):
    r"""A placeholder identity operator that is argument-insensitive.

    Args:
        args: any argument (unused)
        kwargs: any keyword argument (unused)

    Shape:
        - Input: :math:`(*)`, where :math:`*` means any number of dimensions.
        - Output: :math:`(*)`, same shape as the input.

    Examples::

        >>> m = nn.Identity(54, unused_argument1=0.1, unused_argument2=False)
        >>> input = torch.randn(128, 20)
        >>> output = m(input)
        >>> print(output.size())
        torch.Size([128, 20])

    """

    def __init__(self, *args: Any, **kwargs: Any) -> None:
        super().__init__()

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


class Linear(Module):
    r"""Applies an affine linear transformation to the incoming data: :math:`y = xA^T + b`.

    This module supports :ref:`TensorFloat32<tf32_on_ampere>`.

    On certain ROCm devices, when using float16 inputs this module will use :ref:`different precision<fp16_on_mi200>` for backward.

    Args:
        in_features: size of each input sample
        out_features: size of each output sample
        bias: If set to ``False``, the layer will not learn an additive bias.
            Default: ``True``

    Shape:
        - Input: :math:`(*, H_\text{in})` where :math:`*` means any number of
          dimensions including none and :math:`H_\text{in} = \text{in\_features}`.
        - Output: :math:`(*, H_\text{out})` where all but the last dimension
          are the same shape as the input and :math:`H_\text{out} = \text{out\_features}`.

    Attributes:
        weight: the learnable weights of the module of shape
            :math:`(\text{out\_features}, \text{in\_features})`. The values are
            initialized from :math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})`, where
            :math:`k = \frac{1}{\text{in\_features}}`
        bias:   the learnable bias of the module of shape :math:`(\text{out\_features})`.
                If :attr:`bias` is ``True``, the values are initialized from
                :math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})` where
                :math:`k = \frac{1}{\text{in\_features}}`

    Examples::

        >>> m = nn.Linear(20, 30)
        >>> input = torch.randn(128, 20)
        >>> output = m(input)
        >>> print(output.size())
        torch.Size([128, 30])
    """

    __constants__ = ["in_features", "out_features"]
    in_features: int
    out_features: int
    weight: Tensor

    def __init__(
        self,
        in_features: int,
        out_features: int,
        bias: bool = True,
        device=None,
        dtype=None,
    ) -> None:
        factory_kwargs = {"device": device, "dtype": dtype}
        super().__init__()
        self.in_features = in_features
        self.out_features = out_features
        self.weight = Parameter(
            torch.empty((out_features, in_features), **factory_kwargs)
        )
        if bias:
            self.bias = Parameter(torch.empty(out_features, **factory_kwargs))
        else:
            self.register_parameter("bias", None)
        self.reset_parameters()

    def reset_parameters(self) -> None:
        """
        Resets parameters based on their initialization used in ``__init__``.
        """
        # Setting a=sqrt(5) in kaiming_uniform is the same as initializing with
        # uniform(-1/sqrt(in_features), 1/sqrt(in_features)). For details, see
        # https://github.com/pytorch/pytorch/issues/57109
        init.kaiming_uniform_(self.weight, a=math.sqrt(5))
        if self.bias is not None:
            fan_in, _ = init._calculate_fan_in_and_fan_out(self.weight)
            bound = 1 / math.sqrt(fan_in) if fan_in > 0 else 0
            init.uniform_(self.bias, -bound, bound)

    def forward(self, input: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.linear(input, self.weight, self.bias)

    def extra_repr(self) -> str:
        """
        Return the extra representation of the module.
        """
        return f"in_features={self.in_features}, out_features={self.out_features}, bias={self.bias is not None}"


# This class exists solely to avoid triggering an obscure error when scripting
# an improperly quantized attention layer. See this issue for details:
# https://github.com/pytorch/pytorch/issues/58969
# TODO: fail fast on quantization API usage error, then remove this class
# and replace uses of it with plain Linear
class NonDynamicallyQuantizableLinear(Linear):
    def __init__(
        self,
        in_features: int,
        out_features: int,
        bias: bool = True,
        device=None,
        dtype=None,
    ) -> None:
        super().__init__(
            in_features, out_features, bias=bias, device=device, dtype=dtype
        )


class Bilinear(Module):
    r"""Applies a bilinear transformation to the incoming data: :math:`y = x_1^T A x_2 + b`.

    Args:
        in1_features: size of each first input sample, must be > 0
        in2_features: size of each second input sample, must be > 0
        out_features: size of each output sample, must be > 0
        bias: If set to ``False``, the layer will not learn an additive bias.
            Default: ``True``

    Shape:
        - Input1: :math:`(*, H_\text{in1})` where :math:`H_\text{in1}=\text{in1\_features}` and
          :math:`*` means any number of additional dimensions including none. All but the last dimension
          of the inputs should be the same.
        - Input2: :math:`(*, H_\text{in2})` where :math:`H_\text{in2}=\text{in2\_features}`.
        - Output: :math:`(*, H_\text{out})` where :math:`H_\text{out}=\text{out\_features}`
          and all but the last dimension are the same shape as the input.

    Attributes:
        weight: the learnable weights of the module of shape
            :math:`(\text{out\_features}, \text{in1\_features}, \text{in2\_features})`.
            The values are initialized from :math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})`, where
            :math:`k = \frac{1}{\text{in1\_features}}`
        bias:   the learnable bias of the module of shape :math:`(\text{out\_features})`.
                If :attr:`bias` is ``True``, the values are initialized from
                :math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})`, where
                :math:`k = \frac{1}{\text{in1\_features}}`

    Examples::

        >>> m = nn.Bilinear(20, 30, 40)
        >>> input1 = torch.randn(128, 20)
        >>> input2 = torch.randn(128, 30)
        >>> output = m(input1, input2)
        >>> print(output.size())
        torch.Size([128, 40])
    """

    __constants__ = ["in1_features", "in2_features", "out_features"]
    in1_features: int
    in2_features: int
    out_features: int
    weight: Tensor

    def __init__(
        self,
        in1_features: int,
        in2_features: int,
        out_features: int,
        bias: bool = True,
        device=None,
        dtype=None,
    ) -> None:
        factory_kwargs = {"device": device, "dtype": dtype}
        super().__init__()
        if in1_features <= 0:
            raise ValueError(f"in1_features must be > 0, but got {in1_features}")
        self.in1_features = in1_features
        self.in2_features = in2_features
        self.out_features = out_features
        self.weight = Parameter(
            torch.empty((out_features, in1_features, in2_features), **factory_kwargs)
        )

        if bias:
            self.bias = Parameter(torch.empty(out_features, **factory_kwargs))
        else:
            self.register_parameter("bias", None)
        self.reset_parameters()

    def reset_parameters(self) -> None:
        """
        Resets parameters based on their initialization used in ``__init__``.
        """
        bound = 1 / math.sqrt(self.weight.size(1))
        init.uniform_(self.weight, -bound, bound)
        if self.bias is not None:
            init.uniform_(self.bias, -bound, bound)

    def forward(self, input1: Tensor, input2: Tensor) -> Tensor:
        """
        Runs the forward pass.
        """
        return F.bilinear(input1, input2, self.weight, self.bias)

    def extra_repr(self) -> str:
        """
        Return the extra representation of the module.
        """
        return (
            f"in1_features={self.in1_features}, in2_features={self.in2_features}, "
            f"out_features={self.out_features}, bias={self.bias is not None}"
        )


class LazyLinear(LazyModuleMixin, Linear):
    r"""A :class:`torch.nn.Linear` module where `in_features` is inferred.

    In this module, the `weight` and `bias` are of :class:`torch.nn.UninitializedParameter`
    class. They will be initialized after the first call to ``forward`` is done and the
    module will become a regular :class:`torch.nn.Linear` module. The ``in_features`` argument
    of the :class:`Linear` is inferred from the ``input.shape[-1]``.

    Check the :class:`torch.nn.modules.lazy.LazyModuleMixin` for further documentation
    on lazy modules and their limitations.

    Args:
        out_features: size of each output sample
        bias: If set to ``False``, the layer will not learn an additive bias.
            Default: ``True``

    Attributes:
        weight: the learnable weights of the module of shape
            :math:`(\text{out\_features}, \text{in\_features})`. The values are
            initialized from :math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})`, where
            :math:`k = \frac{1}{\text{in\_features}}`
        bias:   the learnable bias of the module of shape :math:`(\text{out\_features})`.
                If :attr:`bias` is ``True``, the values are initialized from
                :math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})` where
                :math:`k = \frac{1}{\text{in\_features}}`


    """

    cls_to_become = Linear  # type: ignore[assignment]
    weight: UninitializedParameter
    bias: UninitializedParameter  # type: ignore[assignment]

    def __init__(
        self, out_features: int, bias: bool = True, device=None, dtype=None
    ) -> None:
        factory_kwargs = {"device": device, "dtype": dtype}
        # bias is hardcoded to False to avoid creating tensor
        # that will soon be overwritten.
        super().__init__(0, 0, False)
        self.weight = UninitializedParameter(**factory_kwargs)
        self.out_features = out_features
        if bias:
            self.bias = UninitializedParameter(**factory_kwargs)

    def reset_parameters(self) -> None:
        """
        Resets parameters based on their initialization used in ``__init__``.
        """
        if not self.has_uninitialized_params() and self.in_features != 0:
            super().reset_parameters()

    def initialize_parameters(self, input) -> None:  # type: ignore[override]
        """
        Infers ``in_features`` based on ``input`` and initializes parameters.
        """
        if self.has_uninitialized_params():
            with torch.no_grad():
                self.in_features = input.shape[-1]
                self.weight.materialize((self.out_features, self.in_features))
                if self.bias is not None:
                    self.bias.materialize((self.out_features,))
                self.reset_parameters()
        if self.in_features == 0:
            assert input.shape[-1] == self.weight.shape[-1], (
                f"The in_features inferred from input: {input.shape[-1]} "
                f"is not equal to in_features from self.weight: "
                f"{self.weight.shape[-1]}"
            )
            self.in_features = input.shape[-1]


# TODO: PartialLinear - maybe in sparse?