[BUG] - unpack error in CUDA extension tutorial

[aur61]

Add Link

https://pytorch.org/tutorials/advanced/cpp_extension.html

Describe the bug

Code to reproduce the issue.

import time

import torch

batch_size = 16
input_features = 32
state_size = 128

# Check if CUDA (GPU) is available
if torch.cuda.is_available():
    # Set the device to CUDA
    device = torch.device("cuda")
    print("CUDA is available. Using GPU.")
else:
    # If CUDA is not available, fall back to CPU
    device = torch.device("cpu")
    print("CUDA is not available. Using CPU.")

X = torch.randn(batch_size, input_features, device=device)
h = torch.randn(batch_size, state_size, device=device)
C = torch.randn(batch_size, state_size, device=device)

rnn = LLTM(input_features, state_size).to(device)

forward = 0
backward = 0
for _ in range(2):
    start = time.time()
    new_h, new_C = rnn(X, (h, C))
    forward += time.time() - start

    start = time.time()
    (new_h.sum() + new_C.sum()).backward()
    backward += time.time() - start

print('Forward: {:.3f} s | Backward {:.3f} s'.format(forward, backward))

Error info:

Traceback (most recent call last):
  File "toy_model.py", line 74, in <module>
    (new_h.sum() + new_C.sum()).backward()
  File "/home/username/miniconda3/envs/tmp/lib/python3.8/site-packages/torch/_tensor.py", line 492, in backward
    torch.autograd.backward(
  File "/home/username/miniconda3/envs/tmp/lib/python3.8/site-packages/torch/autograd/__init__.py", line 251, in backward
    Variable._execution_engine.run_backward(  # Calls into the C++ engine to run the backward pass
  File "/home/username/miniconda3/envs/tmp/lib/python3.8/site-packages/torch/autograd/function.py", line 288, in apply
    return user_fn(self, *args)
  File "toy_model.py", line 25, in backward
    d_old_h, d_input, d_weights, d_bias, d_old_cell = outputs
ValueError: too many values to unpack (expected 5)

Describe your environment

• Platform: Ubuntu
• CUDA: yes
• Pytorch Version: 2.1.0+cu118