title: How to view the functionality of concatenate in Keras?
body: <p>I was looking at the keras merge layers (<a href="https://keras.io/layers/merge/" rel="nofollow noreferrer">https://keras.io/layers/merge/</a>), and wanted to see what each of the layer operations perform. I imagine that their functionality is rather intuitive, but I want to figure out how to view the output for a given example. </p>
  
  <p>To illustrate what I mean, I have two arrays with random input of shape (1,10) and want to see what the output would be if I were to concatenate the two arrays. However, when I do the following, I get the following error: <code>Layer concatenate_18 was called with an input that isn't a symbolic tensor. Received type: &lt;class 'numpy.ndarray'&gt;...All inputs to the layer should be tensors.</code></p>
  
  <pre><code>from keras.layers import concatenate
  data1 = np.random.normal(0, 1, size = (1, 10))
  data2 = np.random.normal(0, 1, size = (1, 10))
  concatenation = concatenate([data1, data2])
  print(concatenation) # I want to print the output of concatenating data1 and data2
  </code></pre>
  
  <p>Based off the message, I am assuming this error has to do with the fact that the inputs are numpy arrays but I am unsure what the appropriate format should be instead? How can I view the output of using concatenate on an example? Thank you!</p>