@tom
Why do target indices outside of [1, C] not lead to an inf-loss or an error?
What happens under the hood?
Example snippet modified:
T = 50 # Input sequence length
C = 20 # Number of classes (including blank)
N = 16 # Batch size
S = 30 # Target sequence length of longest target in batch
S_min = 10 # Minimum target length, for demonstration purposes
input = torch.randn(T, N, C).log_softmax(2).detach().requires_grad_()
# target indices outside of [1, C]
target = torch.randint(low=-10, high=-1, size=(N, S), dtype=torch.long)
input_lengths = torch.full(size=(N,), fill_value=T, dtype=torch.long)
target_lengths = torch.randint(low=S_min, high=S, size=(N,), dtype=torch.long)
ctc_loss = nn.CTCLoss()
loss = ctc_loss(input, target, input_lengths, target_lengths)
print(loss)