model.py 文件源码

def classification_costs(logits, labels, name=None):
    """Compute classification cost mean and classification cost per sample

    Assume unlabeled examples have label == -1. For unlabeled examples, cost == 0.
    Compute the mean over all examples.
    Note that unlabeled examples are treated differently in error calculation.
    """
    with tf.name_scope(name, "classification_costs") as scope:
        applicable = tf.not_equal(labels, -1)

        # Change -1s to zeros to make cross-entropy computable
        labels = tf.where(applicable, labels, tf.zeros_like(labels))

        # This will now have incorrect values for unlabeled examples
        per_sample = tf.nn.sparse_softmax_cross_entropy_with_logits(logits=logits, labels=labels)

        # Retain costs only for labeled
        per_sample = tf.where(applicable, per_sample, tf.zeros_like(per_sample))

        # Take mean over all examples, not just labeled examples.
        labeled_sum = tf.reduce_sum(per_sample)
        total_count = tf.to_float(tf.shape(per_sample)[0])
        mean = tf.div(labeled_sum, total_count, name=scope)

        return mean, per_sample