cls_token.py

# Copyright (c) 2023, NVIDIA CORPORATION.  All rights reserved.
#
# NVIDIA CORPORATION and its licensors retain all intellectual property
# and proprietary rights in and to this software, related documentation
# and any modifications thereto.  Any use, reproduction, disclosure or
# distribution of this software and related documentation without an express
# license agreement from NVIDIA CORPORATION is strictly prohibited.

import torch
from torch import nn


class ClsToken(nn.Module):
    def __init__(self, ndim: int,
                 num_tokens: int = 1,
                 enabled: bool = True,
                 register_multiple: int = 0,
    ):
        super().__init__()

        self.ndim = ndim
        self.enabled = enabled
        self.num_registers = 0
        self.num_tokens = num_tokens
        if enabled:
            if register_multiple > 0:
                self.num_registers = register_multiple - (num_tokens % register_multiple)

            scale = ndim ** -0.5
            self.token = nn.Parameter(torch.randn(num_tokens + self.num_registers, ndim) * scale)
        else:
            self.token = None

        self.num_patches = self.num_tokens + self.num_registers

    def disable(self):
        self.token = None
        self.enabled = False

    def forward(self, x: torch.Tensor):
        if self.token is None:
            return x

        token = self.token.unsqueeze(0).expand(x.shape[0], -1, -1)
        x = torch.cat([
            token,
            x,
        ], dim=1)

        return x

    def no_weight_decay(self):
        return [
            'token',
        ]