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Running
on
Zero
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# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.
import torch
import torch.nn as nn
from torch.nn.init import trunc_normal_
from torch.nn.utils import weight_norm
class DINOHead(nn.Module):
def __init__(
self,
in_dim,
out_dim,
use_bn=False,
nlayers=3,
hidden_dim=2048,
bottleneck_dim=256,
mlp_bias=True,
):
super().__init__()
nlayers = max(nlayers, 1)
self.mlp = _build_mlp(nlayers, in_dim, bottleneck_dim, hidden_dim=hidden_dim, use_bn=use_bn, bias=mlp_bias)
self.apply(self._init_weights)
self.last_layer = weight_norm(nn.Linear(bottleneck_dim, out_dim, bias=False))
self.last_layer.weight_g.data.fill_(1)
def _init_weights(self, m):
if isinstance(m, nn.Linear):
trunc_normal_(m.weight, std=0.02)
if isinstance(m, nn.Linear) and m.bias is not None:
nn.init.constant_(m.bias, 0)
def forward(self, x):
x = self.mlp(x)
eps = 1e-6 if x.dtype == torch.float16 else 1e-12
x = nn.functional.normalize(x, dim=-1, p=2, eps=eps)
x = self.last_layer(x)
return x
def _build_mlp(nlayers, in_dim, bottleneck_dim, hidden_dim=None, use_bn=False, bias=True):
if nlayers == 1:
return nn.Linear(in_dim, bottleneck_dim, bias=bias)
else:
layers = [nn.Linear(in_dim, hidden_dim, bias=bias)]
if use_bn:
layers.append(nn.BatchNorm1d(hidden_dim))
layers.append(nn.GELU())
for _ in range(nlayers - 2):
layers.append(nn.Linear(hidden_dim, hidden_dim, bias=bias))
if use_bn:
layers.append(nn.BatchNorm1d(hidden_dim))
layers.append(nn.GELU())
layers.append(nn.Linear(hidden_dim, bottleneck_dim, bias=bias))
return nn.Sequential(*layers)
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