Edward example code Mixture

Hi all
I am having problems with the example code from http://edwardlib.org/tutorials/unsupervised .

in the section of Criticism.
log_liks = x_post.log_prob(x_broadcasted)
log_liks = tf.reduce_sum(log_liks, 3)

the two code lines,i don’t know the mean.
can you give me some advices?

after the code line : inference.initialize()
inference.n_iter is initialize by 500, i don’t understand this.