tf.summary.scalar
tf.summary.FileWriter
tf.summary.histogram
tf.summary.merge_all
https://www.tensorflow.org/api_docs/python/tf/summary/scalar
https://www.tensorflow.org/api_docs/python/tf/summary/FileWriter
https://www.tensorflow.org/api_docs/python/tf/summary/histogram
https://www.tensorflow.org/api_docs/python/tf/summary/merge_all