def cindex_score(y_true, y_pred):

    g = tf.subtract(tf.expand_dims(y_pred, -1), y_pred)
    g = tf.cast(g == 0.0, tf.float32) * 0.5 + tf.cast(g > 0.0, tf.float32)

    f = tf.subtract(tf.expand_dims(y_true, -1), y_true) > 0.0
    f = tf.matrix_band_part(tf.cast(f, tf.float32), -1, 0)

    g = tf.reduce_sum(tf.multiply(g, f))
    f = tf.reduce_sum(f)

    return tf.where(tf.equal(g, 0), 0.0, g/f)