```
representation = Variable(th.zeros(batch_size , max_length , self.HIDDEN_SIZE * 2))
for i in xrange(batch_size):
for j in xrange(length[i]):
representation[i][j] = th.cat((hidden_forward[max_length - length[i] + j][i]\
, hidden_backward[max_length - 1 - j][i]) , 0)
return representation
```

In short, I want to implement a bi-directional RNN.

hidden_forward and hidden_backward are list of hidden states from previous rnn.

this code yields an error ’ RuntimeError: in-place operations can be only used on variables that don’t share storage with any other variables, but detected that there are 2 objects sharing it’

however, if I replace representation[i][j] with representation[i , j], the code runs just well.

I’m wondering what’s the difference between these two ways to mention a particular part of a high-dimension tensor?