Variable-sized input sequence

[cudacaffe]

Hello there,
I have variable-sized sequences as an input and each token in the sequence is encoded in a D dim vector.
To store the data efficiently they are zero padded, that is, each sequence is stored as a DxM matrix, for
the first sequence, only the first m1 columns are non-zeros, and for the second sequence only the first
m2 columns are non-zeros, and so on.
I was wondering how to feed this kind of input into the network, so the padded part is ignored as it
should be, perhaps by setting "clip" somehow?
Many thanks for your help.
CC

[ParitoshParmar]

In my understanding, in practice, LSTM needs to have fixed length inputs.