code: def CrossEntropySum():
      """Sum of prediction-target cross entropies for multiclass classification."""
      return cb.Serial(
          _CrossEntropy(),
          WeightedSum(),
          name="CrossEntropySum",
          sublayers_to_print=[],
      )
  
imports: from trax import fastmath
  from trax import shapes
  from trax.fastmath import numpy
  from trax.layers import base
  from trax.layers import combinators
  from trax.layers import core
label_desc: Use image node_id 24 for calling a global function with example usage: CrossEntropySum() and returns: cb