Error with inplace operations due to recent changes in pytorch

[jdollinger-bit]

Hi, running the following script with torch=2.0.0:

import unet
import torch
loss_fn = torch.nn.BCEWithLogitsLoss()
input = torch.ones([8, 3, 24, 24])
targets = torch.ones([8, 10, 24, 24])
unet_model = unet.UNet2D(in_channels=3, out_classes=10, residual=True, num_encoding_blocks=2)
out = unet_model(input)
loss = loss_fn(targets, out)
loss.backward()

gave the following error:

---

RuntimeError Traceback (most recent call last)
/tmp/ipykernel_5969/4012461463.py in
5 out = unet_model(input)
6 loss = loss_fn(targets, out)
----> 7 loss.backward()

~/.local/lib/python3.10/site-packages/torch/_tensor.py in backward(self, gradient, retain_graph, create_graph, inputs)
485 inputs=inputs,
486 )
--> 487 torch.autograd.backward(
488 self, gradient, retain_graph, create_graph, inputs=inputs
489 )

~/.local/lib/python3.10/site-packages/torch/autograd/init.py in backward(tensors, grad_tensors, retain_graph, create_graph,
grad_variables, inputs)
198 # some Python versions print out the first line of a multi-line function
199 # calls in the traceback and some print out the last line
--> 200 Variable.execution_engine.run_backward( # Calls into the C++ engine to run the backward pass
201 tensors, grad_tensors, retain_graph, create_graph, inputs,
202 allow_unreachable=True, accumulate_grad=True) # Calls into the C++ engine to run the backward pass

RuntimeError: one of the variables needed for gradient computation has been modified by an inplace operation: [torch.FloatTensor [8, 64, 24, 24]], which is output 0 of ReluBackward0, is at version 1; expected version 0 instead. Hint: enable anomaly detection to find the operation that failed to compute its gradient, with torch.autograd.set_detect_anomaly(True).

Torch does not allow the += operator on tensors anymore.
To fix it, you need to change two lines of code that are considered inplace operations in the newer torch version:
decoding.py l.136: x += connection => x = x + connection
encoding.py l.146: x += connection => x = x + connection
I made a clone of this rep and fixed the error locally this way, but I did not have the permission to push.
Best Regards,
Johannes Dollinger

[fepegar]

Hi, @jdollinger-bit. Thanks for reporting. Can you please fix this in a branch of a fork and open a pull request?