Source code for diffsptk.core.idct

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# Copyright 2022 SPTK Working Group                                        #
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import torch
import torch.nn as nn

from ..misc.utils import numpy_to_torch
from .dct import make_dct_matrix


class InverseDiscreteCosineTransform(nn.Module):
    """See `this page <https://sp-nitech.github.io/sptk/latest/main/idct.html>`_
    for details.

    Parameters
    ----------
    dct_length : int >= 1 [scalar]
        DCT length, :math:`L`.

    """

    def __init__(self, dct_length):
        super(InverseDiscreteCosineTransform, self).__init__()

        assert 1 <= dct_length

        W = make_dct_matrix(dct_length)
        self.register_buffer("W", numpy_to_torch(W.T))

    def forward(self, y):
        """Apply inverse DCT to input.

        Parameters
        ----------
        y : Tensor [shape=(..., L)]
            Input.

        Returns
        -------
        x : Tensor [shape=(..., L)]
            Inverse DCT output.

        Examples
        --------
        >>> x = diffsptk.ramp(3)
        >>> dct = diffsptk.DCT(4)
        >>> idct = diffsptk.IDCT(4)
        >>> x2 = idct(dct(x))
        >>> x2
        tensor([-4.4703e-08,  1.0000e+00,  2.0000e+00,  3.0000e+00])

        """
        x = torch.matmul(y, self.W)
        return x