# Original pytorch implementation by:
# 'MaxViT: Multi-Axis Vision Transformer'
# - https://arxiv.org/pdf/2204.01697.pdf
# Original code by / Copyright 2021, Christoph Reich.
# Modifications & additions by / Copyright 2022 Zilliz. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import torch
[docs]def get_relative_position_index(
win_h: int,
win_w: int
) -> torch.Tensor:
""" Function to generate pair-wise relative position index for each token inside the window.
Taken from Timms Swin V1 implementation.
Args:
win_h (int): Window/Grid height.
win_w (int): Window/Grid width.
Returns:
relative_coords (torch.Tensor): Pair-wise relative position indexes [height * width, height * width].
"""
coords = torch.stack(torch.meshgrid([torch.arange(win_h), torch.arange(win_w)]))
coords_flatten = torch.flatten(coords, 1)
relative_coords = coords_flatten[:, :, None] - coords_flatten[:, None, :]
relative_coords = relative_coords.permute(1, 2, 0).contiguous()
relative_coords[:, :, 0] += win_h - 1
relative_coords[:, :, 1] += win_w - 1
relative_coords[:, :, 0] *= 2 * win_w - 1
return relative_coords.sum(-1)
