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Source code for mmselfsup.models.algorithms.simsiam
# Copyright (c) OpenMMLab. All rights reserved.
import torch.nn as nn
from ..builder import ALGORITHMS, build_backbone, build_head, build_neck
from .base import BaseModel
[docs]@ALGORITHMS.register_module()
class SimSiam(BaseModel):
"""SimSiam.
Implementation of `Exploring Simple Siamese Representation Learning
<https://arxiv.org/abs/2011.10566>`_.
The operation of fixing learning rate of predictor is in
`core/hooks/simsiam_hook.py`.
Args:
backbone (dict): Config dict for module of backbone.
neck (dict): Config dict for module of deep features to compact
feature vectors. Defaults to None.
head (dict): Config dict for module of loss functions.
Defaults to None.
"""
def __init__(self,
backbone,
neck=None,
head=None,
init_cfg=None,
**kwargs):
super(SimSiam, self).__init__(init_cfg)
assert neck is not None
self.encoder = nn.Sequential(
build_backbone(backbone), build_neck(neck))
self.backbone = self.encoder[0]
self.neck = self.encoder[1]
assert head is not None
self.head = build_head(head)
[docs] def extract_feat(self, img):
"""Function to extract features from backbone.
Args:
img (Tensor): Input images of shape (N, C, H, W).
Typically these should be mean centered and std scaled.
Returns:
tuple[Tensor]: backbone outputs.
"""
x = self.backbone(img)
return x
[docs] def forward_train(self, img):
"""Forward computation during training.
Args:
img (list[Tensor]): A list of input images with shape
(N, C, H, W). Typically these should be mean centered
and std scaled.
Returns:
loss[str, Tensor]: A dictionary of loss components
"""
assert isinstance(img, list)
img_v1 = img[0]
img_v2 = img[1]
z1 = self.encoder(img_v1)[0] # NxC
z2 = self.encoder(img_v2)[0] # NxC
losses = 0.5 * (self.head(z1, z2)['loss'] + self.head(z2, z1)['loss'])
return dict(loss=losses)