python - 运行时错误 - 张量的元素 0 不需要 grad 并且没有 grad_fn
问题描述
我正在使用 Unet 模型进行语义分割 - 我有一个 .png 格式的图像及其掩码的自定义数据集。我在网上论坛上找过东西,也试过,但效果不大?有关如何解决错误或改进代码的任何建议都会有所帮助。
model.eval()
with torch.no_grad():
for xb, yb in val_dl:
yb_pred = model(xb.to(device))
# yb_pred = yb_pred["out"].cpu()
print(yb_pred.shape)
yb_pred = torch.argmax(yb_pred,axis = 1)
break
print(yb_pred.shape)
criteron = nn.CrossEntropyLoss(reduction = 'sum')
opt = optim.Adam(model.parameters(), lr = 3e-4)
def loss_batch(loss_func, output, target, opt = None):
loss = loss_func(output, target)
if opt is not None:
opt.zero_grad()
loss.backward()
opt.step()
return loss.item(), None
lr_scheduler = ReduceLROnPlateau(opt, mode = 'min', factor = 0.5, patience= 20, verbose = 1)
def get_lr(opt):
for param_group in opt.param_groups:
return param_group['lr']
current_lr = get_lr(opt)
print('current_lr = {}'.format(current_lr))
def loss_epoch(model, loss_func, dataset_dl, sanity_check = False, opt = None):
running_loss = 0.0
len_data = len(dataset_dl.dataset)
for xb, yb in dataset_dl:
xb = xb.to(device)
yb = yb.to(device)
# xb = torch.tensor(xbh, requires_grad=True)
output = model(xb)
loss_b, metric_b = loss_batch(loss_func, output, yb, opt)
running_loss += loss_b
if sanity_check is True:
break
loss = running_loss/float(len_data)
return loss, None
def train_val(model, params):
num_epochs = params["num_epochs"]
loss_func = params["loss_func"]
opt = params["optimizer"]
train_dl = params["train_dl"]
val_dl = params["val_dl"]
sanity_check = params["sanity_check"]
lr_scheduler = params["lr_scheduler"]
path2weights = params["path2weights"]
loss_history = {"train": [],
"val": []}
best_model_wts = copy.deepcopy(model.state_dict())
best_loss = float('inf')
for epoch in range(num_epochs):
current_lr = get_lr(opt)
print('Epoch {}/{}, current_lr = {}'.format(epoch, num_epochs - 1, current_lr))
with torch.enable_grad():
model.train()
train_loss, _ = loss_epoch(model, loss_func, train_dl, sanity_check, opt)
loss_history["train"].append(train_loss)
model.eval()
with torch.no_grad():
val_loss, _ = loss_epoch(model, loss_func, val_dl, sanity_check, opt)
loss_history["val"].append(val_loss)
if val_loss < best_loss:
best_loss = val_loss
best_model_wts = copy.deepcopy(model.state_dict())
torch.save(model.state_dict(), path2weights)
print("copied best model weights!!")
lr_scheduler.step(val_loss)
if current_lr != get_lr(opt):
print("Loading best model weights!!")
model.load_state_dict(best_model_wts)
print("train Loss: %.6f" %(train_loss))
print("val_loss: %.6f" %(val_loss))
print("-"*20)
model.load_state_dict(best_model_wts)
return model, loss_history, metric_history
path2models = "./models/"
if not os.path.exists(path2models):
os.mkdir(path2models)
param_train = {
"num_epochs": 10,
"loss_func": criteron,
"optimizer": opt,
"train_dl": train_dl,
"val_dl": val_dl,
"sanity_check": False,
"lr_scheduler": lr_scheduler,
"path2weights": path2models + "weights.pt"
model, loss_hist, _ = train_val(model, param_train)
错误消息看起来像 - 文件“”,第 10 行,在模型中,loss_hist,_ = train_val(model, param_train)
文件“”,第 27 行,在 train_val val_loss,_ = loss_epoch(model, loss_func, val_dl, sanity_check, opt)
文件“”,第 13 行,在 loss_epoch loss_b, metric_b = loss_batch(loss_func, output, yb, opt)
文件“”,第 6 行,在 loss_batch loss.backward()
文件“C:\Users\W540\anaconda3\lib\site-packages\torch\tensor.py”,第 198 行,后向 torch.autograd.backward(self,gradient,retain_graph,create_graph)
文件“C:\Users\W540\anaconda3\lib\site-packages\torch\autograd_init _.py ”,第 100 行,后向 allow_unreachable=True) #allow_unreachable 标志
RuntimeError:张量的元素 0 不需要 grad 并且没有 grad_fn
我不确定将哪个变量设置为 require_grad = True 或者我应该在哪里启用 grad ...
解决方案
您可以在此之前尝试loss.backward()
:
loss = Variable(loss, requires_grad = True)
或者,因为变量已从 PyTorch 中删除(仍然存在但已弃用),您只需使用以下代码即可执行相同的操作:
loss.requires_grad = True
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