Calculate sigmoid cross entropy for one-hot lanels and logits.

  Args:
    logits: Tensor of size [batch-size, o=1, p=1, num-classes]
    labels: Tensor of size [batch-size, o=1, p=1, num-classes]
    weights_fn: Function that takes in labels and weighs examples (unused)
  Returns:
    cross_entropy (scalar), weights

def sigmoid_cross_entropy_one_hot(logits, labels, weights_fn=None):
  """Calculate sigmoid cross entropy for one-hot lanels and logits.

  Args:
    logits: Tensor of size [batch-size, o=1, p=1, num-classes]
    labels: Tensor of size [batch-size, o=1, p=1, num-classes]
    weights_fn: Function that takes in labels and weighs examples (unused)
  Returns:
    cross_entropy (scalar), weights
  """
  with tf.variable_scope("sigmoid_cross_entropy_one_hot",
                         values=[logits, labels]):
    del weights_fn
    cross_entropy = tf.losses.sigmoid_cross_entropy(
        multi_class_labels=labels, logits=logits)
    return cross_entropy, tf.constant(1.0)