ctc.py

import torch
import torch.nn.functional as F


class CTC(torch.nn.Module):
    """CTC module.

    Args:
        odim: dimension of outputs
        encoder_output_size: number of encoder projection units
        dropout_rate: dropout rate (0.0 ~ 1.0)
        reduce: reduce the CTC loss into a scalar
    """

    def __init__(
        self,
        odim: int,
        encoder_output_size: int,
        dropout_rate: float = 0.0,
        reduce: bool = True,
        blank_id: int = 0,
        **kwargs,
    ):
        super().__init__()
        eprojs = encoder_output_size
        self.dropout_rate = dropout_rate
        self.ctc_lo = torch.nn.Linear(eprojs, odim)
        self.blank_id = blank_id
        self.ctc_loss = torch.nn.CTCLoss(reduction="none", blank=blank_id)
        self.reduce = reduce

    def softmax(self, hs_pad):
        """softmax of frame activations

        Args:
            Tensor hs_pad: 3d tensor (B, Tmax, eprojs)
        Returns:
            torch.Tensor: softmax applied 3d tensor (B, Tmax, odim)
        """
        return F.softmax(self.ctc_lo(hs_pad), dim=2)

    def log_softmax(self, hs_pad):
        """log_softmax of frame activations

        Args:
            Tensor hs_pad: 3d tensor (B, Tmax, eprojs)
        Returns:
            torch.Tensor: log softmax applied 3d tensor (B, Tmax, odim)
        """
        return F.log_softmax(self.ctc_lo(hs_pad), dim=2)

    def argmax(self, hs_pad):
        """argmax of frame activations

        Args:
            torch.Tensor hs_pad: 3d tensor (B, Tmax, eprojs)
        Returns:
            torch.Tensor: argmax applied 2d tensor (B, Tmax)
        """
        return torch.argmax(self.ctc_lo(hs_pad), dim=2)