docstr: Given the network predictions and targets computed the NLL loss.
code: def compute_objectives(self, predictions, batch, stage):
      "Given the network predictions and targets computed the NLL loss."
      chars, char_lens = batch.char_encoded_eos
      loss = self.hparams.compute_cost(
          predictions, chars, length=char_lens
      )
      return loss
  
file_path: speechbrain/tests/integration/LM_RNN/example_lm_rnn_experiment.py
imports: import math
  import pathlib
  import speechbrain
  from hyperpyyaml import load_hyperpyyaml
label_desc: Use image node_id 2 for calling the LMBrain obj's underlying member method code with example usage: obj.compute_objectives(predictions, batch, stage) and returns: loss