concat failed. Before concat do not need to tf.tile?

[Fisher87]

https://github.com/sjvasquez/quora-duplicate-questions/blob/d93a4bd5edf8327bd5ed7900107ca18bf8bb2b2f/attend.py#L94

a = tf.tile(tf.expand_dims(a, 2), [1, 1, seq_len, 1])
b = tf.tile(tf.expand_dims(b, 1), [1, seq_len, 1, 1])
c = tf.concat([a, b], axis=-1)```