https://stats.stackexchange.com/questions/324992/how-the-embedding-layer-is-trained-in-keras-embedding-layer
https://github.com/keras-team/keras/issues/3110
https://stats.stackexchange.com/questions/324992/how-the-embedding-layer-is-trained-in-keras-embedding-layer
https://github.com/keras-team/keras/issues/3110