note on torch 1.11 vs torch 2.1 compatibility

[BStudent]

(INFORMATIONAL)
Note for users of PyTorch 2.x that this example function works with PyTorch 1.11 but returns nan Loss values under PyTorch 2.1.

UPDATED:

1. This issue only affects conversion of data to pandas DataFrame (for visualization) in the penalization_visualization() demo function.
2. Other code through example_simple_model() demo function appears to work correctly.

Root cause: nan in predict.log() propagates to nan smoothed values when returned as crit(predict.log(), torch.LongTensor([1])).data.

Workaround: replace 0 with 1.0e-10 or similar epsilon-value for plotting (not a real solution due to masking).

• Added context in function docstring below to assist in location.

# NOTE: return value broken WRT PyTorch 2.1, SEE CODE:
def loss(x, crit):
    """
     This function follows the text (by A-T Maintainers):
     > Label smoothing actually starts to penalize the model if it gets
     > very confident about a given choice.
    """
    d = x + 3 * 1
    # predict = torch.FloatTensor([[0, x / d, 1 / d, 1 / d, 1 / d]])
    predict = torch.FloatTensor([[1.0e-10, x / d, 1 / d, 1 / d, 1 / d]])  # <-- workaround

    #   >>> crit(predict.log(), torch.LongTensor([1])).data 
    #   Out: tensor(nan)       # if torch.__version__ == 2.1 
    #   Out: tensor(0.9514)  # if torch.__version__ == 1.11
    return crit(predict.log(), torch.LongTensor([1])).data