BCELoss not accepting lists

1

Hi,

My convLSTM model returns a list of hidden states and my target is a list of 17 images( all tensors)
When the loss function is called, I get the following error:

File “/Users/xyz/opt/anaconda3/envs/matrix/lib/python3.7/site->packages/torch/nn/modules/loss.py”, line 498, in forward
return F.binary_cross_entropy(input, target, weight=self.weight, >reduction=self.reduction)
File “/Users/xyz/opt/anaconda3/envs/matrix/lib/python3.7/site->packages/torch/nn/functional.py”, line 2052, in binary_cross_entropy
if target.size() != input.size():
AttributeError: ‘list’ object has no attribute ‘size’

Part of the training loop:

hc = model.init_hidden(batch_size=1)
for batch_idx, (data, target) in enumerate(train_loader):
    optimizer.zero_grad()
    # Set target, images 2 to 18
    target = data[1:]
    if gpu:
        data = data.cuda()
        target = target.cuda()
        hc.cuda()
    # Get outputs of LSTM
    output = model(data, hc)
    # Calculate loss
    loss = criterion(output, target)
    loss.backward()
    optimizer.step()

How can I fix this?

2

You need to pass torch.Tensor to criterion instead of list
target = torch.Tensor(data[1:])

3

tried that. I’m still getting the same error. May be because ‘output’ is also a list of tensors? I tried casting output the same way. but I get a new error now:

ValueError: only one element tensors can be converted to Python scalars

4

Can you post the full traceback?
From the above traceback, target seems to be the cause for exception.

5

Here you go:

train.py:129: UserWarning: To copy construct from a tensor, it is recommended to use sourceTensor.clone().detach() or sourceTensor.clone().detach().requires_grad_(True), rather than torch.tensor(sourceTensor).
  target = torch.tensor(data[1:])
Traceback (most recent call last):
  File "train.py", line 149, in <module>
    train(epoch)
  File "train.py", line 137, in train
    output = torch.tensor(output)
ValueError: only one element tensors can be converted to Python scalars
6

Can you print shape and type of the variables data, target and hc ?