'''ResNeXt in PyTorch.
See the paper "Aggregated Residual Transformations for Deep Neural Networks" for more details.
'''
import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.autograd import Variable
class Block(nn.Module):
'''Grouped convolution block.'''
expansion = 2
def __init__(self, in_planes, cardinality=32, bottleneck_width=4, stride=1):
super(Block, self).__init__()
group_width = cardinality * bottleneck_width
self.conv1 = nn.Conv2d(in_planes, group_width, kernel_size=1, bias=False)
self.bn1 = nn.BatchNorm2d(group_width)
self.conv2 = nn.Conv2d(group_width, group_width, kernel_size=3, stride=stride, padding=1, groups=cardinality, bias=False)
self.bn2 = nn.BatchNorm2d(group_width)
self.conv3 = nn.Conv2d(group_width, self.expansion*group_width, kernel_size=1, bias=False)
self.bn3 = nn.BatchNorm2d(self.expansion*group_width)
self.shortcut = nn.Sequential()
if stride != 1 or in_planes != self.expansion*group_width:
self.shortcut = nn.Sequential(
nn.Conv2d(in_planes, self.expansion*group_width, kernel_size=1, stride=stride, bias=False),
nn.BatchNorm2d(self.expansion*group_width)
)
def forward(self, x):
out = F.relu(self.bn1(self.conv1(x)))
out = F.relu(self.bn2(self.conv2(out)))
out = self.bn3(self.conv3(out))
out += self.shortcut(x)
out = F.relu(out)
return out
class ResNeXt(nn.Module):
def __init__(self, num_blocks, cardinality, bottleneck_width, num_classes=10):
super(ResNeXt, self).__init__()
self.cardinality = cardinality
self.bottleneck_width = bottleneck_width
self.in_planes = 64
self.conv1 = nn.Conv2d(3, 64, kernel_size=1, bias=False)
self.bn1 = nn.BatchNorm2d(64)
self.layer1 = self._make_layer(num_blocks[0], 1)
self.layer2 = self._make_layer(num_blocks[1], 2)
self.layer3 = self._make_layer(num_blocks[2], 2)
# self.layer4 = self._make_layer(num_blocks[3], 2)
self.linear = nn.Linear(cardinality*bottleneck_width*8, num_classes)
def _make_layer(self, num_blocks, stride):
strides = [stride] + [1]*(num_blocks-1)
layers = []
for stride in strides:
layers.append(Block(self.in_planes, self.cardinality, self.bottleneck_width, stride))
self.in_planes = Block.expansion * self.cardinality * self.bottleneck_width
# Increase bottleneck_width by 2 after each stage.
self.bottleneck_width *= 2
return nn.Sequential(*layers)
def forward(self, x):
out = F.relu(self.bn1(self.conv1(x)))
out = self.layer1(out)
out = self.layer2(out)
out = self.layer3(out)
# out = self.layer4(out)
out = F.avg_pool2d(out, 8)
out = out.view(out.size(0), -1)
out = self.linear(out)
return out
def ResNeXt29_2x64d():
return ResNeXt(num_blocks=[3,3,3], cardinality=2, bottleneck_width=64)
def ResNeXt29_4x64d():
return ResNeXt(num_blocks=[3,3,3], cardinality=4, bottleneck_width=64)
def ResNeXt29_8x64d():
return ResNeXt(num_blocks=[3,3,3], cardinality=8, bottleneck_width=64)
def ResNeXt29_32x4d():
return ResNeXt(num_blocks=[3,3,3], cardinality=32, bottleneck_width=4)
def test_resnext():
net = ResNeXt29_2x64d()
x = torch.randn(1,3,32,32)
y = net(Variable(x))
print(y.size())
# test_resnext()
