import tensorflow as tf

                # element when gathering L_flat into a lower triangular matrix L.
                nb_rows = tf.shape(L_flat)[0]
                zeros = tf.expand_dims(tf.tile(K.zeros((1,)), [nb_rows]), 1)
                try:
                    # Old TF behavior.
                    L_flat = tf.concat(1, [zeros, L_flat])
                except TypeError:
                    # New TF behavior
                    L_flat = tf.concat([zeros, L_flat], 1)

