Multi Criterion Training

[GirinChutia]

Error in Multi Criterion Training

<

weights = [0.2,0.3]
class_weights = torch.FloatTensor(weights).to(device) #.cuda()
criterion = {"CE_Loss1": nn.CrossEntropyLoss(weight=class_weights),"CE_Loss2": nn.CrossEntropyLoss()} 
....
....
loss1 = self.criterion["CE_Loss1"](self.batch["logits1"], self.batch["targets1"])
loss2 = self.criterion["CE_Loss2"](self.batch["logits2"], self.batch["targets2"])
loss_ce1ce2 = loss1 + loss2
self.batch_metrics.update({"loss_ce1": loss1, 
                           "loss_ce2": loss2, 
                           "loss_ce1ce2": loss_ce1ce2})

for key in ["loss_ce1", "loss_ce2", "loss_ce1ce2"]:
        self.meters[key].update(self.batch_metrics[key].item(), self.batch_size)

if self.is_train_loader:
    self.engine.backward(loss_ce1ce2) #causing problem
    self.optimizer.step()
    self.optimizer.zero_grad()

Hi, I am trying to train a model using multi-criterion. Part of code for computing the loss is shown above. Doing so I am getting the following error.

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RuntimeError: Trying to backward through the graph a second time (or directly access saved tensors after they have already been freed). Saved intermediate values of the graph are freed when you call .backward() or autograd.grad(). Specify retain_graph=True if you need to backward through the graph a second time or if you need to access saved tensors after calling backward.

_

Can anyone please check if I am doing the correct way?

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[GirinChutia]

I think I have solved it. Mistake I think I did was, in my runner.train(), I have put callbacks=[dl.BackwardCallback(metric_key="loss_ce1ce2") which shouldn't be there if I put,

if self.is_train_loader:
    self.engine.backward(loss_ce1ce2) 
    self.optimizer.step()
    self.optimizer.zero_grad()

in 'handle_batch' method of my CustomRunner class.

Is my understanding correct? Please let me know.

[Pupy101]

Hi, here is an example of a callback that aggregates several loss functions. I think he should help you

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