Merge pull request #613 from rwightman/mlp-mixer
MLP-Mixer models w/ pretrained weights ported from Google JAX impl...pull/609/head
Ross Wightman
4 years ago
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GitHub
commit
936e9b331d
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""" MLP-Mixer in PyTorch
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Official JAX impl: https://github.com/google-research/vision_transformer/blob/linen/vit_jax/models_mixer.py
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Paper: 'MLP-Mixer: An all-MLP Architecture for Vision' - https://arxiv.org/abs/2105.01601
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@article{tolstikhin2021,
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title={MLP-Mixer: An all-MLP Architecture for Vision},
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author={Tolstikhin, Ilya and Houlsby, Neil and Kolesnikov, Alexander and Beyer, Lucas and Zhai, Xiaohua and Unterthiner,
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Thomas and Yung, Jessica and Keysers, Daniel and Uszkoreit, Jakob and Lucic, Mario and Dosovitskiy, Alexey},
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journal={arXiv preprint arXiv:2105.01601},
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year={2021}
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}
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A thank you to paper authors for releasing code and weights.
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Hacked together by / Copyright 2021 Ross Wightman
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"""
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import math
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from copy import deepcopy
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from functools import partial
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import torch
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import torch.nn as nn
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from timm.data import IMAGENET_DEFAULT_MEAN, IMAGENET_DEFAULT_STD
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from .helpers import build_model_with_cfg, overlay_external_default_cfg
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from .layers import DropPath, to_2tuple, lecun_normal_
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from .registry import register_model
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def _cfg(url='', **kwargs):
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return {
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'url': url,
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'num_classes': 1000, 'input_size': (3, 224, 224), 'pool_size': None,
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'crop_pct': 0.875, 'interpolation': 'bicubic', 'fixed_input_size': True,
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'mean': (0.5, 0.5, 0.5), 'std': (0.5, 0.5, 0.5),
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'first_conv': 'stem.proj', 'classifier': 'head',
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**kwargs
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}
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default_cfgs = dict(
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mixer_s32_224=_cfg(),
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mixer_s16_224=_cfg(),
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mixer_b32_224=_cfg(),
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mixer_b16_224=_cfg(
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url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-vitjx/jx_mixer_b16_224-76587d61.pth',
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),
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mixer_b16_224_in21k=_cfg(
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url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-vitjx/jx_mixer_b16_224_in21k-617b3de2.pth',
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num_classes=21843
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),
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mixer_l32_224=_cfg(),
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mixer_l16_224=_cfg(
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url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-vitjx/jx_mixer_l16_224-92f9adc4.pth',
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),
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mixer_l16_224_in21k=_cfg(
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url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-vitjx/jx_mixer_l16_224_in21k-846aa33c.pth',
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num_classes=21843
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),
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)
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class Mlp(nn.Module):
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""" MLP Block
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NOTE: same impl as ViT, move to common location
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"""
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def __init__(self, in_features, hidden_features=None, out_features=None, act_layer=nn.GELU, drop=0.):
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super().__init__()
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out_features = out_features or in_features
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hidden_features = hidden_features or in_features
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self.fc1 = nn.Linear(in_features, hidden_features)
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self.act = act_layer()
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self.fc2 = nn.Linear(hidden_features, out_features)
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self.drop = nn.Dropout(drop)
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def forward(self, x):
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x = self.fc1(x)
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x = self.act(x)
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x = self.drop(x)
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x = self.fc2(x)
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x = self.drop(x)
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return x
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class PatchEmbed(nn.Module):
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""" Image to Patch Embedding
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NOTE: same impl as ViT, move to common location
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"""
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def __init__(self, img_size=224, patch_size=16, in_chans=3, embed_dim=768, norm_layer=None):
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super().__init__()
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img_size = to_2tuple(img_size)
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patch_size = to_2tuple(patch_size)
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self.img_size = img_size
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self.patch_size = patch_size
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self.patch_grid = (img_size[0] // patch_size[0], img_size[1] // patch_size[1])
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self.num_patches = self.patch_grid[0] * self.patch_grid[1]
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self.proj = nn.Conv2d(in_chans, embed_dim, kernel_size=patch_size, stride=patch_size)
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self.norm = norm_layer(embed_dim) if norm_layer else nn.Identity()
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def forward(self, x):
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B, C, H, W = x.shape
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# FIXME look at relaxing size constraints
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assert H == self.img_size[0] and W == self.img_size[1], \
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f"Input image size ({H}*{W}) doesn't match model ({self.img_size[0]}*{self.img_size[1]})."
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x = self.proj(x).flatten(2).transpose(1, 2)
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x = self.norm(x)
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return x
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class MixerBlock(nn.Module):
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def __init__(
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self, dim, seq_len, tokens_dim, channels_dim,
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norm_layer=partial(nn.LayerNorm, eps=1e-6), act_layer=nn.GELU, drop=0., drop_path=0.):
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super().__init__()
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self.norm1 = norm_layer(dim)
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self.mlp_tokens = Mlp(seq_len, tokens_dim, act_layer=act_layer, drop=drop)
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self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()
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self.norm2 = norm_layer(dim)
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self.mlp_channels = Mlp(dim, channels_dim, act_layer=act_layer, drop=drop)
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def forward(self, x):
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x = x + self.drop_path(self.mlp_tokens(self.norm1(x).transpose(1, 2)).transpose(1, 2))
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x = x + self.drop_path(self.mlp_channels(self.norm2(x)))
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return x
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class MlpMixer(nn.Module):
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def __init__(
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self,
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num_classes=1000,
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img_size=224,
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in_chans=3,
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patch_size=16,
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num_blocks=8,
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hidden_dim=512,
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tokens_dim=256,
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channels_dim=2048,
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norm_layer=partial(nn.LayerNorm, eps=1e-6),
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act_layer=nn.GELU,
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drop=0.,
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drop_path=0.,
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nlhb=False,
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):
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super().__init__()
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self.num_classes = num_classes
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self.stem = PatchEmbed(img_size=img_size, patch_size=patch_size, in_chans=in_chans, embed_dim=hidden_dim)
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# FIXME drop_path (stochastic depth scaling rule?)
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self.blocks = nn.Sequential(*[
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MixerBlock(
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hidden_dim, self.stem.num_patches, tokens_dim, channels_dim,
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norm_layer=norm_layer, act_layer=act_layer, drop=drop, drop_path=drop_path)
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for _ in range(num_blocks)])
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self.norm = norm_layer(hidden_dim)
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self.head = nn.Linear(hidden_dim, self.num_classes) # zero init
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self.init_weights(nlhb=nlhb)
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def init_weights(self, nlhb=False):
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head_bias = -math.log(self.num_classes) if nlhb else 0.
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for n, m in self.named_modules():
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_init_weights(m, n, head_bias=head_bias)
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def forward(self, x):
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x = self.stem(x)
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x = self.blocks(x)
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x = self.norm(x)
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x = x.mean(dim=1)
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x = self.head(x)
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return x
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def _init_weights(m, n: str, head_bias: float = 0.):
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""" Mixer weight initialization (trying to match Flax defaults)
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"""
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if isinstance(m, nn.Linear):
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if n.startswith('head'):
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nn.init.zeros_(m.weight)
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nn.init.constant_(m.bias, head_bias)
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else:
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nn.init.xavier_uniform_(m.weight)
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if m.bias is not None:
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if 'mlp' in n:
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nn.init.normal_(m.bias, std=1e-6)
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else:
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nn.init.zeros_(m.bias)
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elif isinstance(m, nn.Conv2d):
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lecun_normal_(m.weight)
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if m.bias is not None:
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nn.init.zeros_(m.bias)
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elif isinstance(m, nn.LayerNorm):
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nn.init.zeros_(m.bias)
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nn.init.ones_(m.weight)
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def _create_mixer(variant, pretrained=False, default_cfg=None, **kwargs):
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if default_cfg is None:
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default_cfg = deepcopy(default_cfgs[variant])
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overlay_external_default_cfg(default_cfg, kwargs)
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default_num_classes = default_cfg['num_classes']
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default_img_size = default_cfg['input_size'][-2:]
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num_classes = kwargs.pop('num_classes', default_num_classes)
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img_size = kwargs.pop('img_size', default_img_size)
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if kwargs.get('features_only', None):
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raise RuntimeError('features_only not implemented for MLP-Mixer models.')
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model = build_model_with_cfg(
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MlpMixer, variant, pretrained,
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default_cfg=default_cfg,
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img_size=img_size,
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num_classes=num_classes,
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**kwargs)
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return model
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@register_model
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def mixer_s32_224(pretrained=False, **kwargs):
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""" Mixer-S/32 224x224
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"""
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model_args = dict(patch_size=32, num_blocks=8, hidden_dim=512, tokens_dim=256, channels_dim=2048, **kwargs)
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model = _create_mixer('mixer_s32_224', pretrained=pretrained, **model_args)
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return model
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@register_model
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def mixer_s16_224(pretrained=False, **kwargs):
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""" Mixer-S/16 224x224
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"""
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model_args = dict(patch_size=16, num_blocks=8, hidden_dim=512, tokens_dim=256, channels_dim=2048, **kwargs)
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model = _create_mixer('mixer_s16_224', pretrained=pretrained, **model_args)
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return model
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@register_model
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def mixer_b32_224(pretrained=False, **kwargs):
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""" Mixer-B/32 224x224
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"""
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model_args = dict(patch_size=32, num_blocks=12, hidden_dim=768, tokens_dim=384, channels_dim=3072, **kwargs)
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model = _create_mixer('mixer_b32_224', pretrained=pretrained, **model_args)
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return model
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@register_model
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def mixer_b16_224(pretrained=False, **kwargs):
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""" Mixer-B/16 224x224. ImageNet-1k pretrained weights.
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"""
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model_args = dict(patch_size=16, num_blocks=12, hidden_dim=768, tokens_dim=384, channels_dim=3072, **kwargs)
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model = _create_mixer('mixer_b16_224', pretrained=pretrained, **model_args)
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return model
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@register_model
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def mixer_b16_224_in21k(pretrained=False, **kwargs):
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""" Mixer-B/16 224x224. ImageNet-21k pretrained weights.
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"""
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model_args = dict(patch_size=16, num_blocks=12, hidden_dim=768, tokens_dim=384, channels_dim=3072, **kwargs)
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model = _create_mixer('mixer_b16_224_in21k', pretrained=pretrained, **model_args)
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return model
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@register_model
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def mixer_l32_224(pretrained=False, **kwargs):
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""" Mixer-L/32 224x224.
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"""
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model_args = dict(patch_size=32, num_blocks=24, hidden_dim=1024, tokens_dim=512, channels_dim=4096, **kwargs)
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model = _create_mixer('mixer_l32_224', pretrained=pretrained, **model_args)
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return model
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@register_model
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def mixer_l16_224(pretrained=False, **kwargs):
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""" Mixer-L/16 224x224. ImageNet-1k pretrained weights.
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"""
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model_args = dict(patch_size=16, num_blocks=24, hidden_dim=1024, tokens_dim=512, channels_dim=4096, **kwargs)
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model = _create_mixer('mixer_l16_224', pretrained=pretrained, **model_args)
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return model
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@register_model
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def mixer_l16_224_in21k(pretrained=False, **kwargs):
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""" Mixer-L/16 224x224. ImageNet-21k pretrained weights.
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"""
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model_args = dict(patch_size=16, num_blocks=24, hidden_dim=1024, tokens_dim=512, channels_dim=4096, **kwargs)
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model = _create_mixer('mixer_l16_224_in21k', pretrained=pretrained, **model_args)
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return model
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