UnboundLocalError: local variable 'b' referenced before assignment

[ZhiyuanChen]

🐛 Bug

To Reproduce

  File "/opt/conda/lib/python3.10/site-packages/torchmetrics/functional/classification/matthews_corrcoef.py", line 278, in matthews_corrcoef
    return binary_matthews_corrcoef(preds, target, threshold, ignore_index, validate_args)
  File "/opt/conda/lib/python3.10/site-packages/torchmetrics/functional/classification/matthews_corrcoef.py", line 132, in binary_matthews_corrcoef
    return _matthews_corrcoef_reduce(confmat)
  File "/opt/conda/lib/python3.10/site-packages/torchmetrics/functional/classification/matthews_corrcoef.py", line 74, in _matthews_corrcoef_reduce
    numerator = torch.sqrt(eps) * (a - b)

Code sample

# Ideally attach a minimal code sample to reproduce the decried issue.
# Minimal means having the shortest code but still preserving the bug.

Expected behavior

Environment

• TorchMetrics version (if build from source, add commit SHA): ???
• Python & PyTorch Version (e.g., 1.0): ???
• Any other relevant information such as OS (e.g., Linux): ???

Additional context

[ZhiyuanChen]

Thanks! That was quick!