text: """Loss functions."""
  
  import torch.nn as nn
  
  from pycls.core.config import cfg
  
  # Supported loss functions
  _loss_funs = {
      'cross_entropy': nn.CrossEntropyLoss,
  }
  
  def get_loss_fun():
      """Retrieves the loss function."""
      assert cfg.MODEL.LOSS_FUN in _loss_funs.keys(), \
          'Loss function \'{}\' not supported'.format(cfg.TRAIN.LOSS)
      return _loss_funs[cfg.MODEL.LOSS_FUN]().cuda()
  
  
  def register_loss_fun(name, ctor):
      """Registers a loss function dynamically."""
      _loss_funs[name] = ctor
  