Fix: ignore tokens should be set to -100, not -1 #19
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Loss cannot be computed if labels[~masked_indices] = -1. From BertForMaskedLM documentation: "Indices should be in [-100, 0, ..., config.vocab_size] ... Tokens with indices set to -100 are ignored (masked), the loss is only computed for the tokens with labels in [0, ..., config.vocab_size]"
Fix: ignore tokens in target tensor should be set to -100, not -1
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Issue #, if available:
Description of changes:
Correcting the value of unmasked indices in the target tensor in mask_tokens().
Currently, line 348 is: labels[~masked_indices] = -1
But, the value of -1 breaks the loss function. From BertForMaskedLM documentation: "Indices should be in [-100, 0, ..., config.vocab_size] ... Tokens with indices set to -100 are ignored (masked), the loss is only computed for the tokens with labels in [0, ..., config.vocab_size]"
This value constraint appears to hold in every version of the HuggingFace API which has documentation for BertForMaskedLM.
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