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'''EfficientNet in PyTorch.
Paper: "EfficientNet: Rethinking Model Scaling for Convolutional Neural Networks".
Reference: https://github.com/keras-team/keras-applications/blob/master/keras_applications/efficientnet.py
'''
import torch
import torch.nn as nn
import torch.nn.functional as F
def swish(x):
return x * x.sigmoid()
def drop_connect(x, drop_ratio):
keep_ratio = 1.0 - drop_ratio
mask = torch.empty([x.shape[0], 1, 1, 1], dtype=x.dtype, device=x.device)
mask.bernoulli_(keep_ratio)
x.div_(keep_ratio)
x.mul_(mask)
return x
class SE(nn.Module):
'''Squeeze-and-Excitation block with Swish.'''
def __init__(self, in_channels, se_channels):
super(SE, self).__init__()
self.se1 = nn.Conv2d(in_channels, se_channels,
kernel_size=1, bias=True)
self.se2 = nn.Conv2d(se_channels, in_channels,
kernel_size=1, bias=True)
def forward(self, x):
out = F.adaptive_avg_pool2d(x, (1, 1))
out = swish(self.se1(out))
out = self.se2(out).sigmoid()
out = x * out
return out
class Block(nn.Module):
'''expansion + depthwise + pointwise + squeeze-excitation'''
def __init__(self,
in_channels,
out_channels,
kernel_size,
stride,
expand_ratio=1,
se_ratio=0.,
drop_rate=0.):
super(Block, self).__init__()
self.stride = stride
self.drop_rate = drop_rate
self.expand_ratio = expand_ratio
# Expansion
channels = expand_ratio * in_channels
self.conv1 = nn.Conv2d(in_channels,
channels,
kernel_size=1,
stride=1,
padding=0,
bias=False)
self.bn1 = nn.BatchNorm2d(channels)
# Depthwise conv
self.conv2 = nn.Conv2d(channels,
channels,
kernel_size=kernel_size,
stride=stride,
padding=(1 if kernel_size == 3 else 2),
groups=channels,
bias=False)
self.bn2 = nn.BatchNorm2d(channels)
# SE layers
se_channels = int(in_channels * se_ratio)
self.se = SE(channels, se_channels)
# Output
self.conv3 = nn.Conv2d(channels,
out_channels,
kernel_size=1,
stride=1,
padding=0,
bias=False)
self.bn3 = nn.BatchNorm2d(out_channels)
# Skip connection if in and out shapes are the same (MV-V2 style)
self.has_skip = (stride == 1) and (in_channels == out_channels)
def forward(self, x):
out = x if self.expand_ratio == 1 else swish(self.bn1(self.conv1(x)))
out = swish(self.bn2(self.conv2(out)))
out = self.se(out)
out = self.bn3(self.conv3(out))
if self.has_skip:
if self.training and self.drop_rate > 0:
out = drop_connect(out, self.drop_rate)
out = out + x
return out
class EfficientNet(nn.Module):
def __init__(self, cfg, num_classes=10):
super(EfficientNet, self).__init__()
self.cfg = cfg
self.conv1 = nn.Conv2d(3,
32,
kernel_size=3,
stride=1,
padding=1,
bias=False)
self.bn1 = nn.BatchNorm2d(32)
self.layers = self._make_layers(in_channels=32)
self.linear = nn.Linear(cfg['out_channels'][-1], num_classes)
def _make_layers(self, in_channels):
layers = []
cfg = [self.cfg[k] for k in ['expansion', 'out_channels', 'num_blocks', 'kernel_size',
'stride']]
b = 0
blocks = sum(self.cfg['num_blocks'])
for expansion, out_channels, num_blocks, kernel_size, stride in zip(*cfg):
strides = [stride] + [1] * (num_blocks - 1)
for stride in strides:
drop_rate = self.cfg['drop_connect_rate'] * b / blocks
layers.append(
Block(in_channels,
out_channels,
kernel_size,
stride,
expansion,
se_ratio=0.25,
drop_rate=drop_rate))
in_channels = out_channels
return nn.Sequential(*layers)
def forward(self, x):
out = swish(self.bn1(self.conv1(x)))
out = self.layers(out)
out = F.adaptive_avg_pool2d(out, 1)
out = out.view(out.size(0), -1)
dropout_rate = self.cfg['dropout_rate']
if self.training and dropout_rate > 0:
out = F.dropout(out, p=dropout_rate)
out = self.linear(out)
return out
def EfficientNetB0():
cfg = {
'num_blocks': [1, 2, 2, 3, 3, 4, 1],
'expansion': [1, 6, 6, 6, 6, 6, 6],
'out_channels': [16, 24, 40, 80, 112, 192, 320],
'kernel_size': [3, 3, 5, 3, 5, 5, 3],
'stride': [1, 2, 2, 2, 1, 2, 1],
'dropout_rate': 0.2,
'drop_connect_rate': 0.2,
}
return EfficientNet(cfg)
def test():
net = EfficientNetB0()
x = torch.randn(2, 3, 32, 32)
y = net(x)
print(y.shape)
if __name__ == '__main__':
test()
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