Thanks @Prerna_Dhareshwar.
But my only concern here is that this tensors are actually vector representations ( 100 dim vectors) . They are not real sequences.
In that case, for example if I want to pad the first input which is  of dimension torch.Size([1, 100]) , the padded version would be torch.Size([5, 100]) in which all element [1:,:] would be the ‘padding’ index?
Doesn’t it make problem during training?