Cha*_*ker 5 machine-learning deep-learning pytorch
我想实现一个（元）可训练步长。我用这篇文章尝试过：
https://discuss.pytorch.org/t/how-does-one-have-the-parameters-of-a-model-not-be-leafs/70076/17
并与更高的图书馆（https://github.com/facebookresearch/higher）没有运气......
我试过：
eta = torch.tensor([0.5], requires_grad=True).view(1)
inner_opt = torch.optim.Adam(child_model.parameters(), lr=eta)
#meta_params = itertools.chain(child_model.parameters(),eta.parameters())
meta_params = itertools.chain(child_model.parameters())
meta_opt = torch.optim.Adam(meta_params, lr=1e-3)
# do meta-training/outer training minimize outerloop: min_{theta} sum_t L^val( theta^{T} - eta* Grad L^train(theta^{T}) )
nb_outer_steps = 10 # note, in this case it's the same as number of meta-train steps (but it's could not be the same depending how you loop through the val set)
for outer_i, (outer_inputs, outer_targets) in enumerate(testloader, 0):
meta_opt.zero_grad()
if outer_i >= nb_outer_steps:
break
# do inner-training/MAML; minimize innerloop: theta^{T} - eta* Grad L^train(theta^{T}) ~ argmin L^train(theta)
nb_inner_steps = 3
with higher.innerloop_ctx(child_model, inner_opt) as (fmodel, diffopt):
有错误：
Exception has occurred: RuntimeError
Only Tensors created explicitly by the user (graph leaves) support the deepcopy protocol at the moment
无论如何这是行不通的，因为 eta 可能会突然变成负值，所以我真的想用 sigmoid 函数来限制它，但不得不尝试一些东西......
它认为我的步长 NN 不在图中，但这是因为这行代码：
p_new = p + lr*g
group['params'][p_idx] = p_new
但不知怎的，这还不足以有梯度......
完整脚本自包含脚本：
import torch
import torch.nn as nn
from torch.optim.optimizer import Optimizer
import higher
from higher.optim import DifferentiableOptimizer
from higher.optim import DifferentiableSGD
import torchvision
import torchvision.transforms as transforms
from torchviz import make_dot
import copy
import itertools
from collections import OrderedDict
#mini class to add a flatten layer to the ordered dictionary
class Flatten(nn.Module):
def forward(self, input):
'''
Note that input.size(0) is usually the batch size.
So what it does is that given any input with input.size(0) # of batches,
will flatten to be 1 * nb_elements.
'''
batch_size = input.size(0)
out = input.view(batch_size,-1)
return out # (batch_size, *size)
def get_cifar10():
transform = transforms.Compose(
[transforms.ToTensor(),
transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))])
trainset = torchvision.datasets.CIFAR10(root='./data', train=True,
download=True, transform=transform)
trainloader = torch.utils.data.DataLoader(trainset, batch_size=4,
shuffle=True, num_workers=2)
testset = torchvision.datasets.CIFAR10(root='./data', train=False,
download=True, transform=transform)
testloader = torch.utils.data.DataLoader(testset, batch_size=4,
shuffle=False, num_workers=2)
return trainloader, testloader
class MySGD(Optimizer):
def __init__(self, params, eta, prev_lr):
defaults = {'eta':eta, 'prev_lr':prev_lr}
super().__init__(params, defaults)
class TrainableSGD(DifferentiableOptimizer):
def _update(self, grouped_grads, **kwargs):
prev_lr = self.param_groups[0]['prev_lr']
eta = self.param_groups[0]['eta']
# start differentiable & trainable update
zipped = zip(self.param_groups, grouped_grads)
lr = 0.1*eta(prev_lr).view(1)
for group_idx, (group, grads) in enumerate(zipped):
for p_idx, (p, g) in enumerate(zip(group['params'], grads)):
if g is None:
continue
#group['params'][p_idx] = _add(p, -group['lr'], g)
p_new = p + lr*g
group['params'][p_idx] = p_new
# fake returns
self.param_groups[0]['prev_lr'] = lr
higher.register_optim(MySGD, TrainableSGD)
def main():
# get dataloaders
trainloader, testloader = get_cifar10()
criterion = nn.CrossEntropyLoss()
child_model = nn.Sequential(OrderedDict([
('conv1', nn.Conv2d(in_channels=3,out_channels=2,kernel_size=5)),
('relu1', nn.ReLU()),
('Flatten', Flatten()),
('fc', nn.Linear(in_features=28*28*2,out_features=10) )
]))
hidden = torch.randn(size=(1,1),requires_grad=True)
print(f'-> hidden = {hidden}')
eta = nn.Sequential(OrderedDict([
('fc', nn.Linear(1,1)),
('sigmoid', nn.Sigmoid())
]))
inner_opt = MySGD(child_model.parameters(), eta=eta, prev_lr=hidden)
meta_params = itertools.chain(child_model.parameters(),eta.parameters())
#meta_params = itertools.chain(eta.parameters(),[hidden])
meta_opt = torch.optim.Adam(meta_params, lr=1e-3)
# do meta-training/outer training minimize outerloop: min_{theta} sum_t L^val( theta^{T} - eta* Grad L^train(theta^{T}) )
print()
nb_outer_steps = 1 # note, in this case it's the same as number of meta-train steps (but it's could not be the same depending how you loop through the val set)
for outer_i, (outer_inputs, outer_targets) in enumerate(testloader, 0):
meta_opt.zero_grad()
if outer_i >= nb_outer_steps:
break
# do inner-training/MAML; minimize innerloop: theta^{T} - eta * Grad L^train(theta^{T}) ~ argmin L^train(theta)
nb_inner_steps = 3
#with higher.innerloop_ctx(child_model, inner_opt, copy_initial_weights=False) as (fmodel, diffopt):
with higher.innerloop_ctx(child_model, inner_opt) as (fmodel, diffopt):
for inner_i, (inner_inputs, inner_targets) in enumerate(trainloader, 0):
if inner_i >= nb_inner_steps:
break
logits = fmodel(inner_inputs)
inner_loss = criterion(logits, inner_targets)
print(f'--> inner_i = {inner_i}')
print(f'inner_loss^<{inner_i}>: {inner_loss}')
print(f'lr^<{inner_i-1}> = {diffopt.param_groups[0]["prev_lr"]}')
diffopt.step(inner_loss) # changes params P[t+1] using P[t] and loss[t] in a differentiable manner
print(f'lr^<{inner_i}> = {diffopt.param_groups[0]["prev_lr"]}')
print()
# compute the meta-loss L^val( theta^{T} - eta* Grad L^train(theta^{T}) )
outer_outputs = fmodel(outer_inputs)
meta_loss = criterion(outer_outputs, outer_targets) # L^val
make_dot(meta_loss).render('meta_loss',format='png')
meta_loss.backward()
#grad_of_grads = torch.autograd.grad(outputs=meta_loss, inputs=eta.parameters()) # dmeta_loss/dw0
print(f'----> outer_i = {outer_i}')
print(f'-> outer_loss/meta_loss^<{outer_i}>: {meta_loss}')
print(f'child_model.fc.weight.grad = {child_model.fc.weight.grad}')
print(f'hidden.grad = {hidden.grad}')
print(f'eta.fc.weight = {eta.fc.weight.grad}')
meta_opt.step() # meta-optimizer step: more or less theta^<t> := theta^<t> - meta_eta * Grad L^val( theta^{T} - eta* Grad L^train(theta^{T}) )
if __name__ == "__main__":
main()
print('---> Done\a')
注意 None 的：
文件已下载并验证文件已下载并验证->隐藏=张量（[[0.8459]]，requires_grad=True）
--> inner_i = 0 inner_loss^<0>: 2.2696359157562256 lr^<-1> = 张量([[0.8459]], require_grad=True) lr^<0> = 张量([0.0567], grad_fn=)
--> inner_i = 1 inner_loss^<1>: 2.0114920139312744 lr^<0> = 张量([0.0567], grad_fn=) lr^<1> = 张量([0.0720], grad_fn=)
--> inner_i = 2 inner_loss^<2>: 2.3866422176361084 lr^<1> = 张量([0.0720], grad_fn=) lr^<2> = 张量([0.0717], grad_fn=)
---->outer_i=0->outer_loss/meta_loss^<0>:4.021303176879883child_model.fc.weight.grad=无hidden.grad=无eta.fc.weight=无--->完成
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