import tensorflow as tf


            # match attn_dist[batch_size, passage_length] to sparse one-hot representation [batch_size, passage_length, extended_vsize]
            batch_nums = tf.range(0, limit=batch_size) # shape (batch_size)
            batch_nums = tf.expand_dims(batch_nums, axis=1) # shape (batch_size, 1)
            batch_nums = tf.tile(batch_nums, [1, passage_length]) # shape (batch_size, passage_length)
            step_nums = tf.range(0, limit=passage_length) # [passage_length]
