title: What does initial_epoch in Keras mean?
body: <p>I'm a little bit confused about <code>initial_epoch</code> value in <code>fit</code> and <code>fit_generator</code> methods. Here is the <a href="https://keras.io/api/models/model_training_apis/" rel="nofollow noreferrer">doc</a>:</p>
  <blockquote>
  <p><strong>initial_epoch</strong>: Integer. Epoch at which to start training (useful for resuming a previous training run).</p>
  </blockquote>
  <p>I understand, it is not useful if you start training from scratch. It is useful if you trained your dataset and want to improve accuracy or other values (<em>correct me if I'm wrong</em>). But I'm not sure what it really does.</p>
  <p>So after all this, I have 2 questions:</p>
  <ol>
  <li>What does <code>initial_epoch</code> do and what is it for?</li>
  <li>When can I use <code>initial_epoch</code>?</li>
  </ol>
  <ul>
  <li>When I change my dataset?</li>
  <li>When I change the learning rate, optimizer or loss function?</li>
  <li>Both of them?</li>
  </ul>