docstr: Initializes the loss function
  
  :return: output - Initialized cross entropy loss function
docstr_tok: ["Initializes","the","loss","function",":","return",":","output","-","Initialized","cross","entropy","loss","function"]
code: def cross_entropy_loss(self, logits, labels):
      """
      Initializes the loss function
  
      :return: output - Initialized cross entropy loss function
      """
      return F.nll_loss(logits, labels)
  
imports: import logging
  import os
  from argparse import ArgumentParser
  import mlflow
  import mlflow.pytorch
  import pytorch_lightning
  import torch
  from pytorch_lightning.callbacks import LearningRateMonitor
  from pytorch_lightning.callbacks import ModelCheckpoint
  from pytorch_lightning.callbacks.early_stopping import EarlyStopping
  from torch.nn import functional
  from torch.utils.data import DataLoader
  from torch.utils.data import random_split
  from torchvision import datasets
  from torchvision import transforms
label_desc: Use image node_id 4 for calling the LightningMNISTClassifier obj's underlying member method code with example usage: obj.cross_entropy_loss(logits, labels) and returns: F