title: Input shape and Keras
body: <p>I have a set of training data where each input is a vector of length 138. I have 519 of these vectors for a batch size of 519. These are not images, just real-valued numbers.</p>
  
  <p>I'm trying to start with a 2 layer dense Keras model:</p>
  
  <pre><code>model = keras.Sequential([
      layers.Dense(200, activation=tf.nn.relu, input_shape=[138]),
      layers.Dense(200, activation=tf.nn.relu),
      layers.Dense(1)
  ])
  </code></pre>
  
  <p>When I build the model I get the following error:</p>
  
  <pre><code>Error when checking input: expected dense_27_input to have shape (138,) but got array with shape (519,).
  </code></pre>
  
  <p>Where in Keras do I distinguish batch size from number of input features? <code>layers.Dense()</code> seems to assume that my input is in rows vs. columns.</p>