title: ValueError: Dimensions must be equal, but are 64 and 4 for 'MatMul' (op: 'MatMul') with input shapes: [?,64], [4,?]
body: <p>I got an error,</p>
  
  <pre><code>ValueError: Dimensions must be equal, but are 64 and 4 for 'MatMul' (op: 'MatMul') with input shapes: [?,64], [4,?].
  </code></pre>
  
  <p>I wrote codes,</p>
  
  <pre><code>from keras import backend as K
  
  print(input_encoded_m)
  print(question_encoded)
  match = K.dot(input_encoded_m, question_encoded)
  </code></pre>
  
  <p>print(input_encoded_m) shows <code>Tensor("cond_3/Merge:0", shape=(?, 68, 64), dtype=float32)</code> and print(question_encoded) shows <code>Tensor("cond_5/Merge:0", shape=(?, 4, 64), dtype=float32)</code>.I think dot method is not good to calcurate matrix has different rank,so I rewrite</p>
  
  <pre><code>from keras import backend as K
  match = K.get_value(input_encoded_m * question_encoded)
  </code></pre>
  
  <p>But this error occurs:</p>
  
  <pre><code>ValueError: Dimensions must be equal, but are 68 and 4 for 'mul' (op: 'Mul') with input shapes: [?,68,64], [?,4,64]
  </code></pre>
  
  <p>How can I calcurate <code>input_encoded_m</code> &amp; <code>question_encoded</code>? What is wrong ?</p>