pytorch LSTM的dropout參數

pytorch的LSTM及RNN的dropout不會對每個time step進行dropout，只對一層的輸出設置了dropout。
在新版本的pytorch中，對於1層的lstm，dropout參數無效了，就說明對每個時間步是不dropout的。

源碼中，也是最後一層的輸出時才加上的dropout.

for i in range(num_layers):
	all_output = []
	for j, inner in enumerate(inners):
	    l = i * num_directions + j
	
	    hy, output = inner(input, hidden[l], weight[l], batch_sizes)
	    next_hidden.append(hy)
	    all_output.append(output)
	
	input = torch.cat(all_output, input.dim() - 1)
	
	if dropout != 0 and i < num_layers - 1:
	    input = F.dropout(input, p=dropout, training=train, inplace=False)

https://discuss.pytorch.org/t/dropout-in-lstm/7784