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from .module import Module
from .. import functional as F

from torch import Tensor

__all__ = ['ChannelShuffle']

class ChannelShuffle(Module):
    r"""Divides and rearranges the channels in a tensor.



    This operation divides the channels in a tensor of shape :math:`(*, C , H, W)`

    into g groups and rearranges them as :math:`(*, \frac{C}{g}, g, H, W)`,

    while keeping the original tensor shape.



    Args:

        groups (int): number of groups to divide channels in.



    Examples::



        >>> # xdoctest: +IGNORE_WANT("FIXME: incorrect want")

        >>> channel_shuffle = nn.ChannelShuffle(2)

        >>> input = torch.randn(1, 4, 2, 2)

        >>> print(input)

        [[[[1, 2],

           [3, 4]],

          [[5, 6],

           [7, 8]],

          [[9, 10],

           [11, 12]],

          [[13, 14],

           [15, 16]],

         ]]

        >>> output = channel_shuffle(input)

        >>> print(output)

        [[[[1, 2],

           [3, 4]],

          [[9, 10],

           [11, 12]],

          [[5, 6],

           [7, 8]],

          [[13, 14],

           [15, 16]],

         ]]

    """

    __constants__ = ['groups']
    groups: int

    def __init__(self, groups: int) -> None:
        super().__init__()
        self.groups = groups

    def forward(self, input: Tensor) -> Tensor:
        return F.channel_shuffle(input, self.groups)

    def extra_repr(self) -> str:
        return f'groups={self.groups}'