atob model get nan results

[NextGuido]

@costapt Hi, I'm trying to use your code, but I met a problem. During the training process, when I tried to see the atob.png, I found that I only got "a" and no "bp". So I debug the training process and found the result of "bp = atob.predict(a)" is a nan array. May you tell me what's wrong with my training process? Thx