def nonneg_crossentropy(expr, target):
  """A cross entropy operator that is appropriate for NQL outputs.

  Query expressions often evaluate to sparse vectors.  This evaluates cross
  entropy safely.

  Args:
    expr: a Tensorflow expression for some predicted values.
    target: a Tensorflow expression for target values.

  Returns:
    Tensorflow expression for cross entropy.
  """
  expr_replacing_0_with_1 = tf.where(expr > 0, expr,
                                     tf.ones(tf.shape(input=expr), tf.float32))
  cross_entropies = tf.reduce_sum(
      input_tensor=-target * tf.math.log(expr_replacing_0_with_1), axis=1)
  return tf.reduce_mean(input_tensor=cross_entropies, axis=0)
A cross entropy operator that is appropriate for NQL outputs.

  Query expressions often evaluate to sparse vectors.  This evaluates cross
  entropy safely.

  Args:
    expr: a Tensorflow expression for some predicted values.
    target: a Tensorflow expression for target values.

  Returns:
    Tensorflow expression for cross entropy.
  
language/nql/nql/__init__.py