title: How to use Concatenate layers in keras?
body: <p>My code like this:</p>
  
  <pre><code>balabala...
  conv_model.add(keras.layers.Flatten())
  
  input2 = keras.models.Sequential()
  input2.add(keras.layers.Activation('linear', input_shape=(1,)))
  
  model = keras.models.Sequential()
  model.add(keras.layers.Merge([conv_model, input2], mode='concat'))
  balabala.....
  </code></pre>
  
  <p>When I run this code, it says:</p>
  
  <pre><code>UserWarning: The `Merge` layer is deprecated and will be removed after 
  08/2017. Use instead layers from `keras.layers.merge`, e.g. `add`, 
  `concatenate`, etc.
  </code></pre>
  
  <p>I have tried to use 'keras.layers.Concatenate' in many ways like:</p>
  
  <pre><code>model.add(keras.layers.Concatenate([conv_model, angle]))
  </code></pre>
  
  <p>But it says:</p>
  
  <pre><code>The first layer in a Sequential model must get an `input_shape` or 
  `batch_input_shape` argument
  </code></pre>
  
  <p>Is anybody can help?</p>