title: Keras: the difference input_dim and input_length in LSTM
body: <p>In building LSTM, we are required to provide input shape information by:</p>
  
  <pre><code>input_shape = () # a tuple
  </code></pre>
  
  <p>alternatively, by:</p>
  
  <pre><code>input_length = () # an integer
  input_dim = () # an integer
  </code></pre>
  
  <p>I feel a little confused about the two quantities. What are they indicating? </p>
  
  <p>Also, is the input_dim the so-called time steps? </p>