这是我在处理一些合成数据时收到的错误消息。我有点困惑,因为错误仍然存在,尽管我做了别人建议我做的事情。这可能与我没有指定批次有关吗?PyTorch数据集的使用会缓解这个问题吗
这是我的代码(我是PyTorch的新手,现在才开始学习)——它应该是可复制的:
x, y = np.meshgrid(np.random.randn(100) , np.random.randn(100))
z = 2 * x + 3 * y + 1.5 * x * y - x ** 2 - y**2
X = x.ravel().reshape(-1, 1)
Y = y.ravel().reshape(-1, 1)
Z = z.ravel().reshape(-1, 1)
U = np.concatenate([X, Y], axis = 1)
U = torch.tensor(U, requires_grad=True)
Z = torch.tensor(Z, requires_grad=True)
V = []
for i in range(U.shape[0]):
u = U[i, :]
u1 = u.view(-1, 1) @ u.view(1, -1)
u1 = u1.triu()
ones = torch.ones_like(u1)
mask = ones.triu()
mask = (mask == 1)
u2 = torch.masked_select(u1, mask)
u3 = torch.cat([u, u2])
u3 = u3.view(1, -1)
V.append(u3)
V = torch.cat(V, dim = 0)
from torch import nn
from torch import optim
net = nn.Sequential(nn.Linear(V.shape[1], 1))
criterion = nn.MSELoss()
optimizer = optim.SGD(net.parameters(), lr=0.001, momentum=0.9)
for epoch in range(50): # loop over the dataset multiple times
running_loss = 0.0
i = 0
for inputs , labels in zip(V, Z):
# get the inputs; data is a list of [inputs, labels]
# zero the parameter gradients
optimizer.zero_grad()
# forward + backward + optimize
outputs = net(inputs)
loss = criterion(outputs, labels)
loss.backward(retain_graph = True)
optimizer.step()
# print statistics
running_loss += loss.item()
i += 1
if i % 2000 == 1999: # print every 2000 mini-batches
print('[%d, %5d] loss: %.3f' %
(epoch + 1, i + 1, running_loss / 2000))
running_loss = 0.0
print('Finished Training')
---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)
<ipython-input-143-2454f4bb70a5> in <module>
25
26
---> 27 loss.backward(retain_graph = True)
28
29 optimizer.step()
~\Anaconda3\envs\torch\lib\site-packages\torch\tensor.py in backward(self, gradient, retain_graph, create_graph)
193 products. Defaults to ``False``.
194 """
--> 195 torch.autograd.backward(self, gradient, retain_graph, create_graph)
196
197 def register_hook(self, hook):
~\Anaconda3\envs\torch\lib\site-packages\torch\autograd\__init__.py in backward(tensors, grad_tensors, retain_graph, create_graph, grad_variables)
97 Variable._execution_engine.run_backward(
98 tensors, grad_tensors, retain_graph, create_graph,
---> 99 allow_unreachable=True) # allow_unreachable flag
100
101
RuntimeError: Trying to backward through the graph a second time, but the buffers have already been freed. Specify retain_graph=True when calling backward the first time.
你能解释一下错误并修复代码吗
假设您在设置
retain_graph=True
之后没有再次运行数据创建代码,因为它在IPython REPL中。它可以解决这个问题,但在几乎所有情况下,设置retain_graph=True
都不是合适的解决方案在您的例子中,问题是您已经为
U
设置了requires_grad=True
,这意味着在数据创建中涉及U
的所有内容都将记录在计算图中,当调用loss.backward()
时,梯度将通过所有这些内容传播到U
。第一次之后,这些渐变的所有缓冲区都将被释放,第二次后退将失败无论是} 会自动处理
U
还是Z
都不应该有requires_grad=True
,因为它们没有被优化/学习。只有学习到的参数(提供给优化程序的参数)应该有requires_grad=True
,通常也不必手动设置,因为^{您还应该确保从NumPy数据创建的张量的类型为
torch.float
(float32),因为NumPy的浮点数组通常是float64,这通常是不必要的,并且比float32慢,特别是在GPU上并从向后调用中删除
retain_graph=True
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