import tensorflow as tf

    # Step-wise contrastive loss
    even = [2 * i for i in range(25)]
    odd = [2 * i + 1 for i in range(25)]
    pred1 = tf.gather(pred, even)
    pred2 = tf.gather(pred, odd)
    tgt1 = tf.gather(tgt, even)
    tgt2 = tf.gather(tgt, odd)

