pytorch-image-models/timm/models/maxxvit.py

""" MaxVit and CoAtNet Vision Transformer - CNN Hybrids in PyTorch

This is a from-scratch implementation of both CoAtNet and MaxVit in PyTorch.

99% of the implementation was done from papers, however last minute some adjustments were made
based on the (as yet unfinished?) public code release https://github.com/google-research/maxvit

There are multiple sets of models defined for both architectures. Typically, names with a
 `_rw` suffix are my own original configs prior to referencing https://github.com/google-research/maxvit.
These configs work well and appear to be a bit faster / lower resource than the paper.

The models without extra prefix / suffix' (coatnet_0_224, maxvit_tiny_224, etc), are intended to
match paper, BUT, without any official pretrained weights it's difficult to confirm a 100% match.

# FIXME / WARNING
This impl remains a WIP, some configs and models may vanish or change...

Papers:

MaxViT: Multi-Axis Vision Transformer - https://arxiv.org/abs/2204.01697
@article{tu2022maxvit,
  title={MaxViT: Multi-Axis Vision Transformer},
  author={Tu, Zhengzhong and Talebi, Hossein and Zhang, Han and Yang, Feng and Milanfar, Peyman and Bovik, Alan and Li, Yinxiao},
  journal={ECCV},
  year={2022},
}

CoAtNet: Marrying Convolution and Attention for All Data Sizes - https://arxiv.org/abs/2106.04803
@article{DBLP:journals/corr/abs-2106-04803,
  author    = {Zihang Dai and Hanxiao Liu and Quoc V. Le and Mingxing Tan},
  title     = {CoAtNet: Marrying Convolution and Attention for All Data Sizes},
  journal   = {CoRR},
  volume    = {abs/2106.04803},
  year      = {2021}
}

Hacked together by / Copyright 2022, Ross Wightman
"""

import math
from collections import OrderedDict
from dataclasses import dataclass
from functools import partial
from typing import Callable, Optional, Union, Tuple, List

import torch
from torch import nn
from torch.utils.checkpoint import checkpoint

from timm.data import IMAGENET_DEFAULT_MEAN, IMAGENET_DEFAULT_STD
from .helpers import build_model_with_cfg, checkpoint_seq, named_apply
from .fx_features import register_notrace_function
from .layers import Mlp, ConvMlp, DropPath, ClassifierHead, trunc_normal_tf_, LayerNorm2d, LayerNorm
from .layers import create_attn, get_act_layer, get_norm_layer, get_norm_act_layer, create_conv2d
from .layers import to_2tuple, extend_tuple, make_divisible, _assert
from .registry import register_model
from .vision_transformer_relpos import RelPosMlp, RelPosBias  # FIXME move these to common location

__all__ = ['MaxxVitCfg', 'MaxxVitConvCfg', 'MaxxVitTransformerCfg', 'MaxxVit']


def _cfg(url='', **kwargs):
    return {
        'url': url, 'num_classes': 1000, 'input_size': (3, 224, 224), 'pool_size': (7, 7),
        'crop_pct': 0.95, 'interpolation': 'bicubic',
        'mean': (0.5, 0.5, 0.5), 'std': (0.5, 0.5, 0.5),
        'first_conv': 'stem.conv1', 'classifier': 'head.fc',
        'fixed_input_size': True,
        **kwargs
    }


default_cfgs = {
    # Fiddling with configs / defaults / still pretraining
    'coatnet_pico_rw_224': _cfg(url=''),
    'coatnet_nano_rw_224': _cfg(
        url='',
        crop_pct=0.9),
    'coatnet_0_rw_224': _cfg(
        url=''),
    'coatnet_1_rw_224': _cfg(
        url=''
    ),
    'coatnet_2_rw_224': _cfg(url=''),

    # Highly experimental configs
    'coatnet_bn_0_rw_224': _cfg(
        url='',
        mean=IMAGENET_DEFAULT_MEAN, std=IMAGENET_DEFAULT_STD,
        crop_pct=0.95),
    'coatnet_rmlp_nano_rw_224': _cfg(
        url='',
        crop_pct=0.9),
    'coatnet_rmlp_0_rw_224': _cfg(url=''),
    'coatnet_rmlp_1_rw_224': _cfg(
        url=''),
    'coatnet_nano_cc_224': _cfg(url=''),
    'coatnext_nano_rw_224': _cfg(url=''),

    # Trying to be like the CoAtNet paper configs
    'coatnet_0_224': _cfg(url=''),
    'coatnet_1_224': _cfg(url=''),
    'coatnet_2_224': _cfg(url=''),
    'coatnet_3_224': _cfg(url=''),
    'coatnet_4_224': _cfg(url=''),
    'coatnet_5_224': _cfg(url=''),

    # Experimental configs
    'maxvit_pico_rw_256': _cfg(url='', input_size=(3, 256, 256), pool_size=(8, 8)),
    'maxvit_nano_rw_256': _cfg(url='', input_size=(3, 256, 256), pool_size=(8, 8)),
    'maxvit_tiny_rw_224': _cfg(url=''),
    'maxvit_tiny_rw_256': _cfg(url='', input_size=(3, 256, 256), pool_size=(8, 8)),
    'maxvit_tiny_cm_256': _cfg(url='', input_size=(3, 256, 256), pool_size=(8, 8)),
    'maxxvit_nano_rw_256': _cfg(url='', input_size=(3, 256, 256), pool_size=(8, 8)),

    # Trying to be like the MaxViT paper configs
    'maxvit_tiny_224': _cfg(url=''),
    'maxvit_small_224': _cfg(url=''),
    'maxvit_base_224': _cfg(url=''),
    'maxvit_large_224': _cfg(url=''),
    'maxvit_xlarge_224': _cfg(url=''),
}


@dataclass
class MaxxVitTransformerCfg:
    dim_head: int = 32
    expand_ratio: float = 4.0
    expand_first: bool = True
    shortcut_bias: bool = True,
    attn_bias: bool = True
    attn_drop: float = 0.
    proj_drop: float = 0.
    pool_type: str = 'avg'
    rel_pos_type: str = 'bias'
    rel_pos_dim: int = 512  # for relative position types w/ MLP
    window_size: Tuple[int, int] = (7, 7)
    grid_size: Tuple[int, int] = (7, 7)
    init_values: Optional[float] = None
    act_layer: str = 'gelu'
    norm_layer: str = 'layernorm2d'
    norm_layer_cl: str = 'layernorm'
    norm_eps: float = 1e-6


@dataclass
class MaxxVitConvCfg:
    block_type: str = 'mbconv'
    expand_ratio: float = 4.0
    expand_output: bool = True  # calculate expansion channels from output (vs input chs)
    kernel_size: int = 3
    group_size: int = 1  # 1 == depthwise
    pre_norm_act: bool = False  # activation after pre-norm
    output_bias: bool = True  # bias for shortcut + final 1x1 projection conv
    stride_mode: str = 'dw'  # stride done via one of 'pool', '1x1', 'dw'
    pool_type: str = 'avg'
    downsample_pool_type: str = 'avg2'
    attn_early: bool = False  # apply attn between conv2 and norm2, instead of after norm2
    attn_layer: str = 'se'
    attn_act_layer: str = 'silu'
    attn_ratio: float = 0.25
    init_values: Optional[float] = 1e-5  # for ConvNeXt block
    act_layer: str = 'gelu'
    norm_layer: str = ''
    norm_layer_cl: str = ''
    norm_eps: Optional[float] = None

    def __post_init__(self):
        # mbconv vs convnext blocks have different defaults, set in post_init to avoid explicit config args
        assert self.block_type in ('mbconv', 'convnext')
        use_mbconv = self.block_type == 'mbconv'
        if not self.norm_layer:
            self.norm_layer = 'batchnorm2d' if use_mbconv else 'layernorm2d'
        if not self.norm_layer_cl and not use_mbconv:
            self.norm_layer_cl = 'layernorm'
        if self.norm_eps is None:
            self.norm_eps = 1e-5 if use_mbconv else 1e-6
        self.downsample_pool_type = self.downsample_pool_type or self.pool_type


@dataclass
class MaxxVitCfg:
    embed_dim: Tuple[int, ...] = (96, 192, 384, 768)
    depths: Tuple[int, ...] = (2, 3, 5, 2)
    block_type: Tuple[Union[str, Tuple[str, ...]], ...] = ('C', 'C', 'T', 'T')
    stem_width: Union[int, Tuple[int, int]] = 64
    stem_bias: bool = True
    conv_cfg: MaxxVitConvCfg = MaxxVitConvCfg()
    transformer_cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg()
    weight_init: str = 'vit_eff'


def _rw_coat_cfg(
        stride_mode='pool',
        pool_type='avg2',
        conv_output_bias=False,
        conv_attn_early=False,
        conv_norm_layer='',
        transformer_shortcut_bias=True,
        transformer_norm_layer='layernorm2d',
        transformer_norm_layer_cl='layernorm',
        rel_pos_type='bias',
        rel_pos_dim=512,
):
    # 'RW' timm variant models were created and trained before seeing https://github.com/google-research/maxvit
    # Common differences for initial timm models:
    # - pre-norm layer in MZBConv included an activation after norm
    # - mbconv expansion calculated from input instead of output chs
    # - mbconv shortcut and final 1x1 conv did not have a bias
    # - SE act layer was relu, not silu
    # - mbconv uses silu in timm, not gelu
    # - expansion in attention block done via output proj, not input proj
    # Variable differences (evolved over training initial models):
    # - avg pool with kernel_size=2 favoured downsampling (instead of maxpool for coat)
    # - SE attention was between conv2 and norm/act
    # - default to avg pool for mbconv downsample instead of 1x1 or dw conv
    # - transformer block shortcut has no bias
    return dict(
        conv_cfg=MaxxVitConvCfg(
            stride_mode=stride_mode,
            pool_type=pool_type,
            pre_norm_act=True,
            expand_output=False,
            output_bias=conv_output_bias,
            attn_early=conv_attn_early,
            attn_act_layer='relu',
            act_layer='silu',
            norm_layer=conv_norm_layer,
        ),
        transformer_cfg=MaxxVitTransformerCfg(
            expand_first=False,
            shortcut_bias=transformer_shortcut_bias,
            pool_type=pool_type,
            norm_layer=transformer_norm_layer,
            norm_layer_cl=transformer_norm_layer_cl,
            rel_pos_type=rel_pos_type,
            rel_pos_dim=rel_pos_dim,
        ),
    )


def _rw_max_cfg(
        stride_mode='dw',
        pool_type='avg',
        conv_output_bias=False,
        conv_attn_ratio=1 / 16,
        conv_norm_layer='',
        transformer_norm_layer='layernorm2d',
        transformer_norm_layer_cl='layernorm',
        window_size=7,
        dim_head=32,
        rel_pos_type='bias',
        rel_pos_dim=512,
):
    # 'RW' timm variant models were created and trained before seeing https://github.com/google-research/maxvit
    # Differences of initial timm models:
    # - mbconv expansion calculated from input instead of output chs
    # - mbconv shortcut and final 1x1 conv did not have a bias
    # - mbconv uses silu in timm, not gelu
    # - avg pool with kernel_size=2 favoured downsampling (instead of maxpool for coat)
    # - default to avg pool for mbconv downsample instead of 1x1 or dw conv
    # - expansion in attention block done via output proj, not input proj
    return dict(
        conv_cfg=MaxxVitConvCfg(
            stride_mode=stride_mode,
            pool_type=pool_type,
            expand_output=False,
            output_bias=conv_output_bias,
            attn_ratio=conv_attn_ratio,
            act_layer='silu',
            norm_layer=conv_norm_layer,
        ),
        transformer_cfg=MaxxVitTransformerCfg(
            expand_first=False,
            pool_type=pool_type,
            dim_head=dim_head,
            window_size=to_2tuple(window_size),
            grid_size=to_2tuple(window_size),
            norm_layer=transformer_norm_layer,
            norm_layer_cl=transformer_norm_layer_cl,
            rel_pos_type=rel_pos_type,
            rel_pos_dim=rel_pos_dim,
        ),
    )


def _next_cfg(
        stride_mode='dw',
        pool_type='avg2',
        conv_norm_layer='layernorm2d',
        conv_norm_layer_cl='layernorm',
        transformer_norm_layer='layernorm2d',
        transformer_norm_layer_cl='layernorm',
        window_size=7,
        rel_pos_type='bias',
        rel_pos_dim=512,
):
    # For experimental models with convnext instead of mbconv
    return dict(
        conv_cfg=MaxxVitConvCfg(
            block_type='convnext',
            stride_mode=stride_mode,
            pool_type=pool_type,
            expand_output=False,
            norm_layer=conv_norm_layer,
            norm_layer_cl=conv_norm_layer_cl,
        ),
        transformer_cfg=MaxxVitTransformerCfg(
            expand_first=False,
            pool_type=pool_type,
            window_size=to_2tuple(window_size),
            grid_size=to_2tuple(window_size),
            norm_layer=transformer_norm_layer,
            norm_layer_cl=transformer_norm_layer_cl,
            rel_pos_type=rel_pos_type,
            rel_pos_dim=rel_pos_dim,
        ),
    )


model_cfgs = dict(
    # Fiddling with configs / defaults / still pretraining
    coatnet_pico_rw_224=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(2, 3, 5, 2),
        stem_width=(32, 64),
        **_rw_max_cfg(  # using newer max defaults here
            pool_type='avg2',
            conv_output_bias=True,
            conv_attn_ratio=0.25,
        ),
    ),
    coatnet_nano_rw_224=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(3, 4, 6, 3),
        stem_width=(32, 64),
        **_rw_max_cfg(  # using newer max defaults here
            stride_mode='pool',
            pool_type='avg2',
            conv_output_bias=True,
            conv_attn_ratio=0.25,
        ),
    ),
    coatnet_0_rw_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 3, 7, 2),  # deeper than paper '0' model
        stem_width=(32, 64),
        **_rw_coat_cfg(
            conv_attn_early=True,
            transformer_shortcut_bias=False,
        ),
    ),
    coatnet_1_rw_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 6, 14, 2),
        stem_width=(32, 64),
        **_rw_coat_cfg(
            stride_mode='dw',
            conv_attn_early=True,
            transformer_shortcut_bias=False,
        )
    ),
    coatnet_2_rw_224=MaxxVitCfg(
        embed_dim=(128, 256, 512, 1024),
        depths=(2, 6, 14, 2),
        stem_width=(64, 128),
        **_rw_coat_cfg(stride_mode='dw'),
    ),

    # Highly experimental configs
    coatnet_bn_0_rw_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 3, 7, 2),  # deeper than paper '0' model
        stem_width=(32, 64),
        **_rw_coat_cfg(
            stride_mode='dw',
            conv_attn_early=True,
            transformer_shortcut_bias=False,
            transformer_norm_layer='batchnorm2d',
        )
    ),
    coatnet_rmlp_nano_rw_224=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(3, 4, 6, 3),
        stem_width=(32, 64),
        **_rw_max_cfg(
            pool_type='avg2',
            conv_output_bias=True,
            conv_attn_ratio=0.25,
            rel_pos_type='mlp',
            rel_pos_dim=384,
        ),
    ),
    coatnet_rmlp_0_rw_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 3, 7, 2),  # deeper than paper '0' model
        stem_width=(32, 64),
        **_rw_coat_cfg(
            stride_mode='dw',
            rel_pos_type='mlp',
        ),
    ),
    coatnet_rmlp_1_rw_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 6, 14, 2),
        stem_width=(32, 64),
        **_rw_coat_cfg(
            pool_type='max',
            conv_attn_early=True,
            transformer_shortcut_bias=False,
            rel_pos_type='mlp',
            rel_pos_dim=384,  # was supposed to be 512, woops
        ),
    ),
    coatnext_nano_rw_224=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(3, 4, 6, 3),
        stem_width=(32, 64),
        **_next_cfg(),
    ),
    coatnet_nano_cc_224=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(3, 4, 6, 3),
        stem_width=(32, 64),
        block_type=('C', 'C', ('C', 'T'), ('C', 'T')),
        **_rw_coat_cfg(),
    ),

    # Trying to be like the CoAtNet paper configs
    coatnet_0_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 3, 5, 2),
        stem_width=64,
    ),
    coatnet_1_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 6, 14, 2),
        stem_width=64,
    ),
    coatnet_2_224=MaxxVitCfg(
        embed_dim=(128, 256, 512, 1024),
        depths=(2, 6, 14, 2),
        stem_width=128,
    ),
    coatnet_3_224=MaxxVitCfg(
        embed_dim=(192, 384, 768, 1536),
        depths=(2, 6, 14, 2),
        stem_width=192,
    ),
    coatnet_4_224=MaxxVitCfg(
        embed_dim=(192, 384, 768, 1536),
        depths=(2, 12, 28, 2),
        stem_width=192,
    ),
    coatnet_5_224=MaxxVitCfg(
        embed_dim=(256, 512, 1280, 2048),
        depths=(2, 12, 28, 2),
        stem_width=192,
    ),

    # Experimental MaxVit configs
    maxvit_pico_rw_256=MaxxVitCfg(
        embed_dim=(32, 64, 128, 256),
        depths=(2, 2, 5, 2),
        block_type=('M',) * 4,
        stem_width=(24, 32),
        **_rw_max_cfg(window_size=8),
    ),
    maxvit_nano_rw_256=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(1, 2, 3, 1),
        block_type=('M',) * 4,
        stem_width=(32, 64),
        **_rw_max_cfg(window_size=8),
    ),
    maxvit_tiny_rw_224=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(2, 2, 5, 2),
        block_type=('M',) * 4,
        stem_width=(32, 64),
        **_rw_max_cfg(),
    ),
    maxvit_tiny_rw_256=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(2, 2, 5, 2),
        block_type=('M',) * 4,
        stem_width=(32, 64),
        **_rw_max_cfg(window_size=8),
    ),
    maxvit_tiny_cm_256=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(2, 2, 5, 2),
        block_type=('CM',) * 4,
        stem_width=(32, 64),
        **_rw_max_cfg(window_size=8),
    ),
    maxxvit_nano_rw_256=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(1, 2, 3, 1),
        block_type=('M',) * 4,
        stem_width=(32, 64),
        **_next_cfg(window_size=8),
    ),

    # Trying to be like the MaxViT paper configs
    maxvit_tiny_224=MaxxVitCfg(
        embed_dim=(64, 128, 256, 512),
        depths=(2, 2, 5, 2),
        block_type=('M',) * 4,
        stem_width=64,
    ),
    maxvit_small_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 2, 5, 2),
        block_type=('M',) * 4,
        stem_width=64,
    ),
    maxvit_base_224=MaxxVitCfg(
        embed_dim=(96, 192, 384, 768),
        depths=(2, 6, 14, 2),
        block_type=('M',) * 4,
        stem_width=64,
    ),
    maxvit_large_224=MaxxVitCfg(
        embed_dim=(128, 256, 512, 1024),
        depths=(2, 6, 14, 2),
        block_type=('M',) * 4,
        stem_width=128,
    ),
    maxvit_xlarge_224=MaxxVitCfg(
        embed_dim=(192, 384, 768, 1536),
        depths=(2, 6, 14, 2),
        block_type=('M',) * 4,
        stem_width=192,
    ),

)


class Attention2d(nn.Module):
    """ multi-head attention for 2D NCHW tensors"""
    def __init__(
            self,
            dim: int,
            dim_out: Optional[int] = None,
            dim_head: int = 32,
            bias: bool = True,
            expand_first: bool = True,
            rel_pos_cls: Callable = None,
            attn_drop: float = 0.,
            proj_drop: float = 0.
    ):
        super().__init__()
        dim_out = dim_out or dim
        dim_attn = dim_out if expand_first else dim
        self.num_heads = dim_attn // dim_head
        self.dim_head = dim_head
        self.scale = dim_head ** -0.5

        self.qkv = nn.Conv2d(dim, dim_attn * 3, 1, bias=bias)
        self.rel_pos = rel_pos_cls(num_heads=self.num_heads) if rel_pos_cls else None
        self.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Conv2d(dim_attn, dim_out, 1, bias=bias)
        self.proj_drop = nn.Dropout(proj_drop)

    def forward(self, x, shared_rel_pos: Optional[torch.Tensor] = None):
        B, C, H, W = x.shape

        q, k, v = self.qkv(x).view(B, self.num_heads, self.dim_head * 3, -1).chunk(3, dim=2)

        attn = (q.transpose(-2, -1) @ k) * self.scale
        if self.rel_pos is not None:
            attn = self.rel_pos(attn)
        elif shared_rel_pos is not None:
            attn = attn + shared_rel_pos
        attn = attn.softmax(dim=-1)
        attn = self.attn_drop(attn)

        x = (v @ attn.transpose(-2, -1)).view(B, -1, H, W)
        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class AttentionCl(nn.Module):
    """ Channels-last multi-head attention (B, ..., C) """
    def __init__(
            self,
            dim: int,
            dim_out: Optional[int] = None,
            dim_head: int = 32,
            bias: bool = True,
            expand_first: bool = True,
            rel_pos_cls: Callable = None,
            attn_drop: float = 0.,
            proj_drop: float = 0.
    ):
        super().__init__()
        dim_out = dim_out or dim
        dim_attn = dim_out if expand_first and dim_out > dim else dim
        assert dim_attn % dim_head == 0, 'attn dim should be divisible by head_dim'
        self.num_heads = dim_attn // dim_head
        self.dim_head = dim_head
        self.scale = dim_head ** -0.5

        self.qkv = nn.Linear(dim, dim_attn * 3, bias=bias)
        self.rel_pos = rel_pos_cls(num_heads=self.num_heads) if rel_pos_cls else None
        self.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Linear(dim_attn, dim_out, bias=bias)
        self.proj_drop = nn.Dropout(proj_drop)

    def forward(self, x, shared_rel_pos: Optional[torch.Tensor] = None):
        B = x.shape[0]
        restore_shape = x.shape[:-1]

        q, k, v = self.qkv(x).view(B, -1, self.num_heads, self.dim_head * 3).transpose(1, 2).chunk(3, dim=3)

        attn = (q @ k.transpose(-2, -1)) * self.scale
        if self.rel_pos is not None:
            attn = self.rel_pos(attn, shared_rel_pos=shared_rel_pos)
        elif shared_rel_pos is not None:
            attn = attn + shared_rel_pos
        attn = attn.softmax(dim=-1)
        attn = self.attn_drop(attn)

        x = (attn @ v).transpose(1, 2).reshape(restore_shape + (-1,))
        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class LayerScale(nn.Module):
    def __init__(self, dim, init_values=1e-5, inplace=False):
        super().__init__()
        self.inplace = inplace
        self.gamma = nn.Parameter(init_values * torch.ones(dim))

    def forward(self, x):
        gamma = self.gamma
        return x.mul_(gamma) if self.inplace else x * gamma


class LayerScale2d(nn.Module):
    def __init__(self, dim, init_values=1e-5, inplace=False):
        super().__init__()
        self.inplace = inplace
        self.gamma = nn.Parameter(init_values * torch.ones(dim))

    def forward(self, x):
        gamma = self.gamma.view(1, -1, 1, 1)
        return x.mul_(gamma) if self.inplace else x * gamma


class Downsample2d(nn.Module):
    """ A downsample pooling module for Coat that handles 2d <-> 1d conversion
    """

    def __init__(
            self,
            dim: int,
            dim_out: int,
            pool_type: str = 'avg2',
            bias: bool = True,
    ):
        super().__init__()
        assert pool_type in ('max', 'avg', 'avg2')
        if pool_type == 'max':
            self.pool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
        elif pool_type == 'avg':
            self.pool = nn.AvgPool2d(kernel_size=3, stride=2, padding=1, count_include_pad=False)
        else:
            self.pool = nn.AvgPool2d(2)

        if dim != dim_out:
            self.expand = nn.Conv2d(dim, dim_out, 1, bias=bias)
        else:
            self.expand = nn.Identity()

    def forward(self, x):
        x = self.pool(x)  # spatial downsample
        x = self.expand(x)  # expand chs
        return x


def _init_transformer(module, name, scheme=''):
    if isinstance(module, (nn.Conv2d, nn.Linear)):
        if scheme == 'normal':
            nn.init.normal_(module.weight, std=.02)
            if module.bias is not None:
                nn.init.zeros_(module.bias)
        elif scheme == 'trunc_normal':
            trunc_normal_tf_(module.weight, std=.02)
            if module.bias is not None:
                nn.init.zeros_(module.bias)
        elif scheme == 'xavier_normal':
            nn.init.xavier_normal_(module.weight)
            if module.bias is not None:
                nn.init.zeros_(module.bias)
        else:
            # vit like
            nn.init.xavier_uniform_(module.weight)
            if module.bias is not None:
                if 'mlp' in name:
                    nn.init.normal_(module.bias, std=1e-6)
                else:
                    nn.init.zeros_(module.bias)


class TransformerBlock2d(nn.Module):
    """ Transformer block with 2D downsampling
    '2D' NCHW tensor layout
    """

    def __init__(
            self,
            dim: int,
            dim_out: int,
            stride: int = 1,
            rel_pos_cls: Callable = None,
            cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg(),
            drop_path: float = 0.,
    ):
        super().__init__()
        norm_layer = partial(get_norm_layer(cfg.norm_layer), eps=cfg.norm_eps)
        act_layer = get_act_layer(cfg.act_layer)

        if stride == 2:
            self.shortcut = Downsample2d(dim, dim_out, pool_type=cfg.pool_type, bias=cfg.shortcut_bias)
            self.norm1 = nn.Sequential(OrderedDict([
                ('norm', norm_layer(dim)),
                ('down', Downsample2d(dim, dim, pool_type=cfg.pool_type)),
            ]))
        else:
            assert dim == dim_out
            self.shortcut = nn.Identity()
            self.norm1 = norm_layer(dim)

        self.attn = Attention2d(
            dim,
            dim_out,
            dim_head=cfg.dim_head,
            expand_first=cfg.expand_first,
            bias=cfg.attn_bias,
            rel_pos_cls=rel_pos_cls,
            attn_drop=cfg.attn_drop,
            proj_drop=cfg.proj_drop
        )
        self.ls1 = LayerScale2d(dim_out, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path1 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

        self.norm2 = norm_layer(dim_out)
        self.mlp = ConvMlp(
            in_features=dim_out,
            hidden_features=int(dim_out * cfg.expand_ratio),
            act_layer=act_layer,
            drop=cfg.proj_drop)
        self.ls2 = LayerScale2d(dim_out, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path2 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

    def init_weights(self, scheme=''):
        named_apply(partial(_init_transformer, scheme=scheme), self)

    def forward(self, x, shared_rel_pos: Optional[torch.Tensor] = None):
        x = self.shortcut(x) + self.drop_path1(self.ls1(self.attn(self.norm1(x), shared_rel_pos=shared_rel_pos)))
        x = x + self.drop_path2(self.ls2(self.mlp(self.norm2(x))))
        return x


def _init_conv(module, name, scheme=''):
    if isinstance(module, nn.Conv2d):
        if scheme == 'normal':
            nn.init.normal_(module.weight, std=.02)
            if module.bias is not None:
                nn.init.zeros_(module.bias)
        elif scheme == 'trunc_normal':
            trunc_normal_tf_(module.weight, std=.02)
            if module.bias is not None:
                nn.init.zeros_(module.bias)
        elif scheme == 'xavier_normal':
            nn.init.xavier_normal_(module.weight)
            if module.bias is not None:
                nn.init.zeros_(module.bias)
        else:
            # efficientnet like
            fan_out = module.kernel_size[0] * module.kernel_size[1] * module.out_channels
            fan_out //= module.groups
            nn.init.normal_(module.weight, 0, math.sqrt(2.0 / fan_out))
            if module.bias is not None:
                nn.init.zeros_(module.bias)


def num_groups(group_size, channels):
    if not group_size:  # 0 or None
        return 1  # normal conv with 1 group
    else:
        # NOTE group_size == 1 -> depthwise conv
        assert channels % group_size == 0
        return channels // group_size


class MbConvBlock(nn.Module):
    """ Pre-Norm Conv Block - 1x1 - kxk - 1x1, w/ inverted bottleneck (expand)
    """
    def __init__(
            self,
            in_chs: int,
            out_chs: int,
            stride: int = 1,
            dilation: Tuple[int, int] = (1, 1),
            cfg: MaxxVitConvCfg = MaxxVitConvCfg(),
            drop_path: float = 0.
    ):
        super(MbConvBlock, self).__init__()
        norm_act_layer = partial(get_norm_act_layer(cfg.norm_layer, cfg.act_layer), eps=cfg.norm_eps)
        mid_chs = make_divisible((out_chs if cfg.expand_output else in_chs) * cfg.expand_ratio)
        groups = num_groups(cfg.group_size, mid_chs)

        if stride == 2:
            self.shortcut = Downsample2d(in_chs, out_chs, pool_type=cfg.pool_type, bias=cfg.output_bias)
        else:
            self.shortcut = nn.Identity()

        assert cfg.stride_mode in ('pool', '1x1', 'dw')
        stride_pool, stride_1, stride_2 = 1, 1, 1
        if cfg.stride_mode == 'pool':
            # NOTE this is not described in paper, experiment to find faster option that doesn't stride in 1x1
            stride_pool, dilation_2 = stride, dilation[1]
            # FIXME handle dilation of avg pool
        elif cfg.stride_mode == '1x1':
            # NOTE I don't like this option described in paper, 1x1 w/ stride throws info away
            stride_1, dilation_2 = stride, dilation[1]
        else:
            stride_2, dilation_2 = stride, dilation[0]

        self.pre_norm = norm_act_layer(in_chs, apply_act=cfg.pre_norm_act)
        if stride_pool > 1:
            self.down = Downsample2d(in_chs, in_chs, pool_type=cfg.downsample_pool_type)
        else:
            self.down = nn.Identity()
        self.conv1_1x1 = create_conv2d(in_chs, mid_chs, 1, stride=stride_1)
        self.norm1 = norm_act_layer(mid_chs)

        self.conv2_kxk = create_conv2d(
            mid_chs, mid_chs, cfg.kernel_size, stride=stride_2, dilation=dilation_2, groups=groups)

        attn_kwargs = {}
        if isinstance(cfg.attn_layer, str):
            if cfg.attn_layer == 'se' or cfg.attn_layer == 'eca':
                attn_kwargs['act_layer'] = cfg.attn_act_layer
                attn_kwargs['rd_channels'] = int(cfg.attn_ratio * (out_chs if cfg.expand_output else mid_chs))

        # two different orderings for SE and norm2 (due to some weights and trials using SE before norm2)
        if cfg.attn_early:
            self.se_early = create_attn(cfg.attn_layer, mid_chs, **attn_kwargs)
            self.norm2 = norm_act_layer(mid_chs)
            self.se = None
        else:
            self.se_early = None
            self.norm2 = norm_act_layer(mid_chs)
            self.se = create_attn(cfg.attn_layer, mid_chs, **attn_kwargs)

        self.conv3_1x1 = create_conv2d(mid_chs, out_chs, 1, bias=cfg.output_bias)
        self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()

    def init_weights(self, scheme=''):
        named_apply(partial(_init_conv, scheme=scheme), self)

    def forward(self, x):
        shortcut = self.shortcut(x)
        x = self.pre_norm(x)
        x = self.down(x)

        # 1x1 expansion conv & norm-act
        x = self.conv1_1x1(x)
        x = self.norm1(x)

        # depthwise / grouped 3x3 conv w/ SE (or other) channel attention & norm-act
        x = self.conv2_kxk(x)
        if self.se_early is not None:
            x = self.se_early(x)
        x = self.norm2(x)
        if self.se is not None:
            x = self.se(x)

        # 1x1 linear projection to output width
        x = self.conv3_1x1(x)
        x = self.drop_path(x) + shortcut
        return x


class ConvNeXtBlock(nn.Module):
    """ ConvNeXt Block
    """

    def __init__(
            self,
            in_chs: int,
            out_chs: Optional[int] = None,
            kernel_size: int = 7,
            stride: int = 1,
            dilation: Tuple[int, int] = (1, 1),
            cfg: MaxxVitConvCfg = MaxxVitConvCfg(),
            conv_mlp: bool = True,
            drop_path: float = 0.
    ):
        super().__init__()
        out_chs = out_chs or in_chs
        act_layer = get_act_layer(cfg.act_layer)
        if conv_mlp:
            norm_layer = partial(get_norm_layer(cfg.norm_layer), eps=cfg.norm_eps)
            mlp_layer = ConvMlp
        else:
            assert 'layernorm' in cfg.norm_layer
            norm_layer = LayerNorm
            mlp_layer = Mlp
        self.use_conv_mlp = conv_mlp

        if stride == 2:
            self.shortcut = Downsample2d(in_chs, out_chs)
        elif in_chs != out_chs:
            self.shortcut = nn.Conv2d(in_chs, out_chs, kernel_size=1, bias=cfg.output_bias)
        else:
            self.shortcut = nn.Identity()

        assert cfg.stride_mode in ('pool', 'dw')
        stride_pool, stride_dw = 1, 1
        # FIXME handle dilation?
        if cfg.stride_mode == 'pool':
            stride_pool = stride
        else:
            stride_dw = stride

        if stride_pool == 2:
            self.down = Downsample2d(in_chs, in_chs, pool_type=cfg.downsample_pool_type)
        else:
            self.down = nn.Identity()

        self.conv_dw = create_conv2d(
            in_chs, out_chs, kernel_size=kernel_size, stride=stride_dw, dilation=dilation[1],
            depthwise=True, bias=cfg.output_bias)
        self.norm = norm_layer(out_chs)
        self.mlp = mlp_layer(out_chs, int(cfg.expand_ratio * out_chs), bias=cfg.output_bias, act_layer=act_layer)
        if conv_mlp:
            self.ls = LayerScale2d(out_chs, cfg.init_values) if cfg.init_values else nn.Identity()
        else:
            self.ls = LayerScale(out_chs, cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()

    def forward(self, x):
        shortcut = self.shortcut(x)
        x = self.down(x)
        x = self.conv_dw(x)
        if self.use_conv_mlp:
            x = self.norm(x)
            x = self.mlp(x)
            x = self.ls(x)
        else:
            x = x.permute(0, 2, 3, 1)
            x = self.norm(x)
            x = self.mlp(x)
            x = self.ls(x)
            x = x.permute(0, 3, 1, 2)

        x = self.drop_path(x) + shortcut
        return x


def window_partition(x, window_size: List[int]):
    B, H, W, C = x.shape
    _assert(H % window_size[0] == 0, f'height ({H}) must be divisible by window ({window_size[0]})')
    _assert(W % window_size[1] == 0, '')
    x = x.view(B, H // window_size[0], window_size[0], W // window_size[1], window_size[1], C)
    windows = x.permute(0, 1, 3, 2, 4, 5).contiguous().view(-1, window_size[0], window_size[1], C)
    return windows


@register_notrace_function  # reason: int argument is a Proxy
def window_reverse(windows, window_size: List[int], img_size: List[int]):
    H, W = img_size
    C = windows.shape[-1]
    x = windows.view(-1, H // window_size[0], W // window_size[1], window_size[0], window_size[1], C)
    x = x.permute(0, 1, 3, 2, 4, 5).contiguous().view(-1, H, W, C)
    return x


def grid_partition(x, grid_size: List[int]):
    B, H, W, C = x.shape
    _assert(H % grid_size[0] == 0, f'height {H} must be divisible by grid {grid_size[0]}')
    _assert(W % grid_size[1] == 0, '')
    x = x.view(B, grid_size[0], H // grid_size[0], grid_size[1], W // grid_size[1], C)
    windows = x.permute(0, 2, 4, 1, 3, 5).contiguous().view(-1, grid_size[0], grid_size[1], C)
    return windows


@register_notrace_function  # reason: int argument is a Proxy
def grid_reverse(windows, grid_size: List[int], img_size: List[int]):
    H, W = img_size
    C = windows.shape[-1]
    x = windows.view(-1, H // grid_size[0], W // grid_size[1], grid_size[0], grid_size[1], C)
    x = x.permute(0, 3, 1, 4, 2, 5).contiguous().view(-1, H, W, C)
    return x


def get_rel_pos_cls(cfg: MaxxVitTransformerCfg, window_size):
    rel_pos_cls = None
    if cfg.rel_pos_type == 'mlp':
        rel_pos_cls = partial(RelPosMlp, window_size=window_size, hidden_dim=cfg.rel_pos_dim)
    elif cfg.rel_pos_type == 'bias':
        rel_pos_cls = partial(RelPosBias, window_size=window_size)
    return rel_pos_cls


class PartitionAttention(nn.Module):
    """ Grid or Block partition + Attn + FFN.
    NxC tensor layout.
    """

    def __init__(
            self,
            dim: int,
            partition_type: str = 'block',
            cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg(),
            drop_path: float = 0.,
    ):
        super().__init__()
        norm_layer = partial(get_norm_layer(cfg.norm_layer_cl), eps=cfg.norm_eps)  # NOTE this block is channels-last
        act_layer = get_act_layer(cfg.act_layer)

        self.partition_block = partition_type == 'block'
        self.partition_size = to_2tuple(cfg.window_size if self.partition_block else cfg.grid_size)
        rel_pos_cls = get_rel_pos_cls(cfg, self.partition_size)

        self.norm1 = norm_layer(dim)
        self.attn = AttentionCl(
            dim,
            dim,
            dim_head=cfg.dim_head,
            bias=cfg.attn_bias,
            rel_pos_cls=rel_pos_cls,
            attn_drop=cfg.attn_drop,
            proj_drop=cfg.proj_drop,
        )
        self.ls1 = LayerScale(dim, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path1 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

        self.norm2 = norm_layer(dim)
        self.mlp = Mlp(
            in_features=dim,
            hidden_features=int(dim * cfg.expand_ratio),
            act_layer=act_layer,
            drop=cfg.proj_drop)
        self.ls2 = LayerScale(dim, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path2 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

    def _partition_attn(self, x):
        img_size = x.shape[1:3]
        if self.partition_block:
            partitioned = window_partition(x, self.partition_size)
        else:
            partitioned = grid_partition(x, self.partition_size)

        partitioned = self.attn(partitioned)

        if self.partition_block:
            x = window_reverse(partitioned, self.partition_size, img_size)
        else:
            x = grid_reverse(partitioned, self.partition_size, img_size)
        return x

    def forward(self, x):
        x = x + self.drop_path1(self.ls1(self._partition_attn(self.norm1(x))))
        x = x + self.drop_path2(self.ls2(self.mlp(self.norm2(x))))
        return x


class CombinedPartitionAttention(nn.Module):
    """ Experimental. Grid and Block partition + single FFN
    NxC tensor layout.
    """

    def __init__(
            self,
            dim: int,
            cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg(),
            drop_path: float = 0.,
    ):
        super().__init__()
        assert dim % 2 == 0
        norm_layer = partial(get_norm_layer(cfg.norm_layer_cl), eps=cfg.norm_eps)  # NOTE this block is channels-last
        act_layer = get_act_layer(cfg.act_layer)

        assert cfg.window_size == cfg.grid_size
        self.partition_size = to_2tuple(cfg.window_size)
        rel_pos_cls = get_rel_pos_cls(cfg, self.partition_size)

        self.norm1 = norm_layer(dim)
        self.attn_block = AttentionCl(
            dim,
            dim // 2,
            dim_head=cfg.dim_head,
            bias=cfg.attn_bias,
            rel_pos_cls=rel_pos_cls,
            attn_drop=cfg.attn_drop,
            proj_drop=cfg.proj_drop,
        )
        self.attn_grid = AttentionCl(
            dim,
            dim // 2,
            dim_head=cfg.dim_head,
            bias=cfg.attn_bias,
            rel_pos_cls=rel_pos_cls,
            attn_drop=cfg.attn_drop,
            proj_drop=cfg.proj_drop,
        )
        self.ls1 = LayerScale(dim, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path1 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

        self.norm2 = norm_layer(dim)
        self.mlp = Mlp(
            in_features=dim,
            hidden_features=int(dim * cfg.expand_ratio),
            out_features=dim,
            act_layer=act_layer,
            drop=cfg.proj_drop)
        self.ls2 = LayerScale(dim, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path2 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

    def _partition_attn(self, x):
        img_size = x.shape[1:3]

        partitioned_block = window_partition(x, self.partition_size)
        partitioned_block = self.attn_block(partitioned_block)
        x_window = window_reverse(partitioned_block, self.partition_size, img_size)

        partitioned_grid = grid_partition(x, self.partition_size)
        partitioned_grid = self.attn_grid(partitioned_grid)
        x_grid = grid_reverse(partitioned_grid, self.partition_size, img_size)

        return torch.cat([x_window, x_grid], dim=-1)

    def forward(self, x):
        x = x + self.drop_path1(self.ls1(self._partition_attn(self.norm1(x))))
        x = x + self.drop_path2(self.ls2(self.mlp(self.norm2(x))))
        return x


def window_partition_nchw(x, window_size: List[int]):
    B, C, H, W = x.shape
    _assert(H % window_size[0] == 0, f'height ({H}) must be divisible by window ({window_size[0]})')
    _assert(W % window_size[1] == 0, '')
    x = x.view(B, C, H // window_size[0], window_size[0], W // window_size[1], window_size[1])
    windows = x.permute(0, 2, 4, 1, 3, 5).contiguous().view(-1, C, window_size[0], window_size[1])
    return windows


@register_notrace_function  # reason: int argument is a Proxy
def window_reverse_nchw(windows, window_size: List[int], img_size: List[int]):
    H, W = img_size
    C = windows.shape[1]
    x = windows.view(-1, H // window_size[0], W // window_size[1], C, window_size[0], window_size[1])
    x = x.permute(0, 3, 1, 4, 2, 5).contiguous().view(-1, C, H, W)
    return x


def grid_partition_nchw(x, grid_size: List[int]):
    B, C, H, W = x.shape
    _assert(H % grid_size[0] == 0, f'height {H} must be divisible by grid {grid_size[0]}')
    _assert(W % grid_size[1] == 0, '')
    x = x.view(B, C, grid_size[0], H // grid_size[0], grid_size[1], W // grid_size[1])
    windows = x.permute(0, 3, 5, 1, 2, 4).contiguous().view(-1, C, grid_size[0], grid_size[1])
    return windows


@register_notrace_function  # reason: int argument is a Proxy
def grid_reverse_nchw(windows, grid_size: List[int], img_size: List[int]):
    H, W = img_size
    C = windows.shape[1]
    x = windows.view(-1, H // grid_size[0], W // grid_size[1], C, grid_size[0], grid_size[1])
    x = x.permute(0, 3, 4, 1, 5, 2).contiguous().view(-1, C, H, W)
    return x


class PartitionAttention2d(nn.Module):
    """ Grid or Block partition + Attn + FFN
    '2D' NCHW tensor layout.
    """

    def __init__(
            self,
            dim: int,
            partition_type: str = 'block',
            cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg(),
            drop_path: float = 0.,
    ):
        super().__init__()
        norm_layer = partial(get_norm_layer(cfg.norm_layer), eps=cfg.norm_eps)  # NOTE this block is channels-last
        act_layer = get_act_layer(cfg.act_layer)

        self.partition_block = partition_type == 'block'
        self.partition_size = to_2tuple(cfg.window_size if self.partition_block else cfg.grid_size)
        rel_pos_cls = get_rel_pos_cls(cfg, self.partition_size)

        self.norm1 = norm_layer(dim)
        self.attn = Attention2d(
            dim,
            dim,
            dim_head=cfg.dim_head,
            bias=cfg.attn_bias,
            rel_pos_cls=rel_pos_cls,
            attn_drop=cfg.attn_drop,
            proj_drop=cfg.proj_drop,
        )
        self.ls1 = LayerScale2d(dim, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path1 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

        self.norm2 = norm_layer(dim)
        self.mlp = ConvMlp(
            in_features=dim,
            hidden_features=int(dim * cfg.expand_ratio),
            act_layer=act_layer,
            drop=cfg.proj_drop)
        self.ls2 = LayerScale2d(dim, init_values=cfg.init_values) if cfg.init_values else nn.Identity()
        self.drop_path2 = DropPath(drop_path) if drop_path > 0. else nn.Identity()

    def _partition_attn(self, x):
        img_size = x.shape[-2:]
        if self.partition_block:
            partitioned = window_partition_nchw(x, self.partition_size)
        else:
            partitioned = grid_partition_nchw(x, self.partition_size)

        partitioned = self.attn(partitioned)

        if self.partition_block:
            x = window_reverse_nchw(partitioned, self.partition_size, img_size)
        else:
            x = grid_reverse_nchw(partitioned, self.partition_size, img_size)
        return x

    def forward(self, x):
        x = x + self.drop_path1(self.ls1(self._partition_attn(self.norm1(x))))
        x = x + self.drop_path2(self.ls2(self.mlp(self.norm2(x))))
        return x


class MaxxVitBlock(nn.Module):
    """
    """

    def __init__(
            self,
            dim: int,
            dim_out: int,
            stride: int = 1,
            conv_cfg: MaxxVitConvCfg = MaxxVitConvCfg(),
            transformer_cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg(),
            use_nchw_attn: bool = False,  # FIXME move to cfg? True is ~20-30% faster on TPU, 5-10% slower on GPU
            drop_path: float = 0.,
    ):
        super().__init__()

        conv_cls = ConvNeXtBlock if conv_cfg.block_type == 'convnext' else MbConvBlock
        self.conv = conv_cls(dim, dim_out, stride=stride, cfg=conv_cfg, drop_path=drop_path)

        attn_kwargs = dict(dim=dim_out, cfg=transformer_cfg, drop_path=drop_path)
        partition_layer = PartitionAttention2d if use_nchw_attn else PartitionAttention
        self.nchw_attn = use_nchw_attn
        self.attn_block = partition_layer(**attn_kwargs)
        self.attn_grid = partition_layer(partition_type='grid', **attn_kwargs)

    def init_weights(self, scheme=''):
        named_apply(partial(_init_transformer, scheme=scheme), self.attn_block)
        named_apply(partial(_init_transformer, scheme=scheme), self.attn_grid)
        named_apply(partial(_init_conv, scheme=scheme), self.conv)

    def forward(self, x):
        # NCHW format
        x = self.conv(x)

        if not self.nchw_attn:
            x = x.permute(0, 2, 3, 1)  # to NHWC (channels-last)
        x = self.attn_block(x)
        x = self.attn_grid(x)
        if not self.nchw_attn:
            x = x.permute(0, 3, 1, 2)  # back to NCHW
        return x


class CombinedMaxxVitBlock(nn.Module):
    """
    """

    def __init__(
            self,
            dim,
            dim_out,
            stride=1,
            num_conv=2,
            conv_cfg: MaxxVitConvCfg = MaxxVitConvCfg(),
            transformer_cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg(),
            drop_path=0.,
    ):
        super().__init__()

        conv_cls = ConvNeXtBlock if conv_cfg.block_type == 'convnext' else MbConvBlock
        if num_conv > 1:
            convs = [conv_cls(dim, dim_out, stride=stride, cfg=conv_cfg, drop_path=drop_path)]
            convs += [conv_cls(dim_out, dim_out, cfg=conv_cfg, drop_path=drop_path)] * (num_conv - 1)
            self.conv = nn.Sequential(*convs)
        else:
            self.conv = conv_cls(dim, dim_out, stride=stride, cfg=conv_cfg, drop_path=drop_path)
        self.attn = CombinedPartitionAttention(dim=dim_out, cfg=transformer_cfg, drop_path=drop_path)

    def init_weights(self, scheme=''):
        named_apply(partial(_init_transformer, scheme=scheme), self.attn)
        named_apply(partial(_init_conv, scheme=scheme), self.conv)

    def forward(self, x):
        x = self.conv(x)
        x = x.permute(0, 2, 3, 1)
        x = self.attn(x)
        x = x.permute(0, 3, 1, 2)
        return x


class MaxxVitStage(nn.Module):
    def __init__(
            self,
            in_chs: int,
            out_chs: int,
            stride: int = 2,
            depth: int = 4,
            feat_size: Tuple[int, int] = (14, 14),
            block_types: Union[str, Tuple[str]] = 'C',
            transformer_cfg: MaxxVitTransformerCfg = MaxxVitTransformerCfg(),
            conv_cfg: MaxxVitConvCfg = MaxxVitConvCfg(),
            drop_path: Union[float, List[float]] = 0.,
    ):
        super().__init__()
        self.grad_checkpointing = False

        block_types = extend_tuple(block_types, depth)
        blocks = []
        for i, t in enumerate(block_types):
            block_stride = stride if i == 0 else 1
            assert t in ('C', 'T', 'M', 'CM')
            if t == 'C':
                conv_cls = ConvNeXtBlock if conv_cfg.block_type == 'convnext' else MbConvBlock
                blocks += [conv_cls(
                    in_chs,
                    out_chs,
                    stride=block_stride,
                    cfg=conv_cfg,
                    drop_path=drop_path[i],
                )]
            elif t == 'T':
                rel_pos_cls = get_rel_pos_cls(transformer_cfg, feat_size)
                blocks += [TransformerBlock2d(
                    in_chs,
                    out_chs,
                    stride=block_stride,
                    rel_pos_cls=rel_pos_cls,
                    cfg=transformer_cfg,
                    drop_path=drop_path[i],
                )]
            elif t == 'M':
                blocks += [MaxxVitBlock(
                    in_chs,
                    out_chs,
                    stride=block_stride,
                    conv_cfg=conv_cfg,
                    transformer_cfg=transformer_cfg,
                    drop_path=drop_path[i],
                )]
            elif t == 'CM':
                blocks += [CombinedMaxxVitBlock(
                    in_chs,
                    out_chs,
                    stride=block_stride,
                    conv_cfg=conv_cfg,
                    transformer_cfg=transformer_cfg,
                    drop_path=drop_path[i],
                )]
            in_chs = out_chs
        self.blocks = nn.Sequential(*blocks)

    def forward(self, x):
        if self.grad_checkpointing and not torch.jit.is_scripting():
            x = checkpoint_seq(self.blocks, x)
        else:
            x = self.blocks(x)
        return x


class Stem(nn.Module):

    def __init__(
            self,
            in_chs: int,
            out_chs: int,
            kernel_size: int = 3,
            act_layer: str = 'gelu',
            norm_layer: str = 'batchnorm2d',
            norm_eps: float = 1e-5,
    ):
        super().__init__()
        if not isinstance(out_chs, (list, tuple)):
            out_chs = to_2tuple(out_chs)

        norm_act_layer = partial(get_norm_act_layer(norm_layer, act_layer), eps=norm_eps)
        self.out_chs = out_chs[-1]
        self.stride = 2

        self.conv1 = create_conv2d(in_chs, out_chs[0], kernel_size, stride=2)
        self.norm1 = norm_act_layer(out_chs[0])
        self.conv2 = create_conv2d(out_chs[0], out_chs[1], kernel_size, stride=1)

    @torch.jit.ignore
    def init_weights(self, scheme=''):
        named_apply(partial(_init_conv, scheme=scheme), self)

    def forward(self, x):
        x = self.conv1(x)
        x = self.norm1(x)
        x = self.conv2(x)
        return x


class MaxxVit(nn.Module):
    """
    """

    def __init__(
            self,
            cfg: MaxxVitCfg,
            img_size: Union[int, Tuple[int, int]] = 224,
            in_chans: int = 3,
            num_classes: int = 1000,
            global_pool: str = 'avg',
            drop_rate: float = 0.,
            drop_path_rate: float = 0.
    ):
        super().__init__()
        img_size = to_2tuple(img_size)
        self.num_classes = num_classes
        self.global_pool = global_pool
        self.num_features = cfg.embed_dim[-1]
        self.embed_dim = cfg.embed_dim
        self.drop_rate = drop_rate
        self.grad_checkpointing = False

        self.stem = Stem(
            in_chs=in_chans,
            out_chs=cfg.stem_width,
            act_layer=cfg.conv_cfg.act_layer,
            norm_layer=cfg.conv_cfg.norm_layer,
            norm_eps=cfg.conv_cfg.norm_eps,
        )

        stride = self.stem.stride
        feat_size = tuple([i // s for i, s in zip(img_size, to_2tuple(stride))])

        num_stages = len(cfg.embed_dim)
        assert len(cfg.depths) == num_stages
        dpr = [x.tolist() for x in torch.linspace(0, drop_path_rate, sum(cfg.depths)).split(cfg.depths)]
        in_chs = self.stem.out_chs
        stages = []
        for i in range(num_stages):
            stage_stride = 2
            out_chs = cfg.embed_dim[i]
            feat_size = tuple([(r - 1) // stage_stride + 1 for r in feat_size])
            stages += [MaxxVitStage(
                in_chs,
                out_chs,
                depth=cfg.depths[i],
                block_types=cfg.block_type[i],
                conv_cfg=cfg.conv_cfg,
                transformer_cfg=cfg.transformer_cfg,
                feat_size=feat_size,
                drop_path=dpr[i],
            )]
            stride *= stage_stride
            in_chs = out_chs
        self.stages = nn.Sequential(*stages)

        final_norm_layer = get_norm_layer(cfg.transformer_cfg.norm_layer)
        self.norm = final_norm_layer(self.num_features, eps=cfg.transformer_cfg.norm_eps)

        # Classifier head
        self.head = ClassifierHead(self.num_features, num_classes, pool_type=global_pool, drop_rate=drop_rate)

        # Weight init (default PyTorch init works well for AdamW if scheme not set)
        assert cfg.weight_init in ('', 'normal', 'trunc_normal', 'xavier_normal', 'vit_eff')
        if cfg.weight_init:
            named_apply(partial(self._init_weights, scheme=cfg.weight_init), self)

    def _init_weights(self, module, name, scheme=''):
        if hasattr(module, 'init_weights'):
            try:
                module.init_weights(scheme=scheme)
            except TypeError:
                module.init_weights()

    @torch.jit.ignore
    def no_weight_decay(self):
        return {
            k for k, _ in self.named_parameters()
            if any(n in k for n in ["relative_position_bias_table", "rel_pos.mlp"])}

    @torch.jit.ignore
    def group_matcher(self, coarse=False):
        matcher = dict(
            stem=r'^stem',  # stem and embed
            blocks=[(r'^stages\.(\d+)', None), (r'^norm', (99999,))]
        )
        return matcher

    @torch.jit.ignore
    def set_grad_checkpointing(self, enable=True):
        for s in self.stages:
            s.grad_checkpointing = enable

    @torch.jit.ignore
    def get_classifier(self):
        return self.head.fc

    def reset_classifier(self, num_classes, global_pool=None):
        self.num_classes = num_classes
        if global_pool is None:
            global_pool = self.head.global_pool.pool_type
        self.head = ClassifierHead(self.num_features, num_classes, pool_type=global_pool, drop_rate=self.drop_rate)

    def forward_features(self, x):
        x = self.stem(x)
        x = self.stages(x)
        x = self.norm(x)
        return x

    def forward_head(self, x, pre_logits: bool = False):
        return self.head(x, pre_logits=pre_logits)

    def forward(self, x):
        x = self.forward_features(x)
        x = self.forward_head(x)
        return x


def _create_maxxvit(variant, cfg_variant=None, pretrained=False, **kwargs):
    return build_model_with_cfg(
        MaxxVit, variant, pretrained,
        model_cfg=model_cfgs[variant] if not cfg_variant else model_cfgs[cfg_variant],
        feature_cfg=dict(flatten_sequential=True),
        **kwargs)


@register_model
def coatnet_pico_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_pico_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_nano_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_nano_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_0_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_0_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_1_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_1_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_2_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_2_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_bn_0_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_bn_0_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_rmlp_nano_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_rmlp_nano_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_rmlp_0_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_rmlp_0_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_rmlp_1_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_rmlp_1_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_nano_cc_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_nano_cc_224', pretrained=pretrained, **kwargs)


@register_model
def coatnext_nano_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnext_nano_rw_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_0_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_0_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_1_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_1_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_2_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_2_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_3_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_3_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_4_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_4_224', pretrained=pretrained, **kwargs)


@register_model
def coatnet_5_224(pretrained=False, **kwargs):
    return _create_maxxvit('coatnet_5_224', pretrained=pretrained, **kwargs)


@register_model
def maxvit_pico_rw_256(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_pico_rw_256', pretrained=pretrained, **kwargs)


@register_model
def maxvit_nano_rw_256(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_nano_rw_256', pretrained=pretrained, **kwargs)


@register_model
def maxvit_tiny_rw_224(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_tiny_rw_224', pretrained=pretrained, **kwargs)


@register_model
def maxvit_tiny_rw_256(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_tiny_rw_256', pretrained=pretrained, **kwargs)


@register_model
def maxvit_tiny_cm_256(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_tiny_cm_256', pretrained=pretrained, **kwargs)


@register_model
def maxxvit_nano_rw_256(pretrained=False, **kwargs):
    return _create_maxxvit('maxxvit_nano_rw_256', pretrained=pretrained, **kwargs)


@register_model
def maxvit_tiny_224(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_tiny_224', pretrained=pretrained, **kwargs)


@register_model
def maxvit_small_224(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_small_224', pretrained=pretrained, **kwargs)


@register_model
def maxvit_base_224(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_base_224', pretrained=pretrained, **kwargs)


@register_model
def maxvit_large_224(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_large_224', pretrained=pretrained, **kwargs)


@register_model
def maxvit_xlarge_224(pretrained=False, **kwargs):
    return _create_maxxvit('maxvit_xlarge_224', pretrained=pretrained, **kwargs)