title: How to retrain a neural network in Keras without restart the jupyter notebook?
body: <p>I constructed a simple neural network using Keras. And when I run it in jupyter notebook for the first time, I works perfectly well. But If I rerun it without changing anything, some problems happens. The following two pictures showing the screenshot for the first time and second time respectively. You can see the difference.
  <a href="https://i.stack.imgur.com/aJWcg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aJWcg.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/AdEf7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AdEf7.png" alt="enter image description here"></a>
  I'm a newbie to Keras and have searched the Internet for several hours. What should I do so that I can rerun the neural network without restart jupyter notebook? Thanks！</p>