Thank you for your quick response, but the word features in a context of RNN is still unclear to me. The GRU doc says,

input : A (seq_len x batch x input_size) tensor containing the features of the input sequence.

and

input_size – The number of expected features in the input x

For example, if you input a sequence
[[[ 0.1,  0.2]],
 [[ 0.1,  0.2]],
 [[ 0.3,  0.1]]]

, then seq_len is 3, batch is 1 and input_size i.e. features is 2?